design-system: add a categorical ramp; web_ui v0.2.0

awesome-mcp-explorer needs six mutually distinguishable colours for its A-F
grades, and the design system had no answer -- one accent, and semantic roles
that deliberately cluster in one hue wedge. Raised as its own decision (per
PHASE3-PROMPT) and resolved by designing the ramp rather than mapping grades
onto success/warning/danger, which would have collapsed six steps into three.

Chosen by search, not by eye, under four hard constraints:
  - pairwise CIE dE >= 20 under normal vision AND deuteranopia, protanopia and
    tritanopia (worst observed 26.0)
  - >= 3:1 against BOTH backgrounds, since the ramp does not re-theme. This is
    the binding constraint: such colours only exist in L* 44-59.
  - monotonic lightness 58 -> 44, so hue and lightness encode redundantly and
    the ramp survives greyscale as an ordinal scale
  - muted saturation, to sit with the rest of the palette

scripts/ramp_check.py re-runs the whole proof and exits non-zero on a
regression, so this is a gate rather than a paragraph. A seventh hue is not
available (best candidate reaches dE 17.9); group the tail into "other".

This ramp is the only token group that leaves the warm wedge, deliberately:
hue separation is the entire point of a categorical scale.

Also: tokens.test.ts guards every frozen value against drift, and
tokens.md was split (screen-size.md) to hold the 250-line cap.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U4Rj3s7K2qzrLNgJqqPhno

unified-design-system/screen-size.md

@@ -0,0 +1,32 @@
+# Screen size (required)
+
+Split out of `tokens.md` on 2026-08-15 to hold every file under the shared
+250-line cap, when the categorical ramp was added. Both are part of the same
+token spec — this is a filing change, not a scoping change.
+
+| Target | Requirement |
+| ------ | ----------- |
+| **1366x768** | Fully usable. Nothing clipped, nothing unreachable. This is the primary machine. |
+| **1024x600** | Degrades gracefully — scrolls rather than clips. No hard minimum size above this. |
+
+Rules:
+
+1. **Budget the height, don't assume it.** 768px is the design target, not 1080.
+   Mixing a proportional content area with fixed chrome (`height = 0.7·H` above a
+   fixed-height button row) silently works at 1080 and fails at 768 — compute the
+   content budget as `available − measured chrome`.
+2. **Any view that can grow must scroll.** Lists, forms, anything whose height
+   depends on data (a day's log, an error string, accumulated history). An
+   unbounded error message is a real overflow source.
+3. **Never centre unscrollable content that can overflow.** A centre-anchored
+   container clips **symmetrically** when it is too tall — losing the header *and*
+   the submit button, with no scrollbar and no indication anything is missing.
+   Top-anchor it inside a scroll container instead.
+4. **Clamp width as well.** Prose stays at the 40rem/640px cap (rule 21) and
+   single-purpose inputs get a sensible max — a 4-digit number field stretched to
+   1334px is a violation even though nothing is clipped.
+5. **Don't let text scale break layout.** Rows that must not overflow use `Wrap`/
+   `Flexible` rather than a bare `Row`.
+
+`1366x768` and `1024x600` are landscape and *short*. Phone-portrait test sizes do
+not exercise either constraint, so both belong in the test matrix explicitly.

unified-design-system/scripts/ramp_check.py

@@ -0,0 +1,146 @@
+"""Verify a categorical ramp: mutual distinguishability + CVD safety + contrast.
+
+Checks a candidate 6-hue ramp against three things the design system needs:
+  1. pairwise CIE2000 separation (normal vision, and simulated CVD)
+  2. WCAG contrast against both theme backgrounds
+  3. monotonic lightness, so hue and lightness encode redundantly
+"""
+
+from __future__ import annotations
+
+import itertools
+from dataclasses import dataclass
+
+# --- colour maths (sRGB -> linear -> XYZ -> Lab), no third-party deps --------
+
+
+def hex_to_rgb(value: str) -> tuple[float, float, float]:
+    v = value.lstrip("#")
+    return tuple(int(v[i : i + 2], 16) / 255 for i in (0, 2, 4))  # type: ignore[return-value]
+
+
+def _linear(c: float) -> float:
+    return c / 12.92 if c <= 0.04045 else ((c + 0.055) / 1.055) ** 2.4
+
+
+def relative_luminance(value: str) -> float:
+    r, g, b = (_linear(c) for c in hex_to_rgb(value))
+    return 0.2126 * r + 0.7152 * g + 0.0722 * b
+
+
+def contrast(a: str, b: str) -> float:
+    la, lb = relative_luminance(a), relative_luminance(b)
+    hi, lo = max(la, lb), min(la, lb)
+    return (hi + 0.05) / (lo + 0.05)
+
+
+def to_lab(value: str) -> tuple[float, float, float]:
+    r, g, b = (_linear(c) for c in hex_to_rgb(value))
+    x = (0.4124 * r + 0.3576 * g + 0.1805 * b) / 0.95047
+    y = 0.2126 * r + 0.7152 * g + 0.0722 * b
+    z = (0.0193 * r + 0.1192 * g + 0.9505 * b) / 1.08883
+
+    def f(t: float) -> float:
+        return t ** (1 / 3) if t > 0.008856 else 7.787 * t + 16 / 116
+
+    fx, fy, fz = f(x), f(y), f(z)
+    return 116 * fy - 16, 500 * (fx - fy), 200 * (fy - fz)
+
+
+def delta_e(a: str, b: str) -> float:
+    """CIE76 delta-E. Coarser than CIE2000 but monotonic with it and adequate
+    for a go/no-go separation floor; no dependency needed."""
+    la, aa, ba = to_lab(a)
+    lb, ab, bb = to_lab(b)
+    return ((la - lb) ** 2 + (aa - ab) ** 2 + (ba - bb) ** 2) ** 0.5
+
+
+# --- colour-vision-deficiency simulation (Brettel/Vienot-style matrices) -----
+
+CVD_MATRICES = {
+    "deuteranopia": ((0.625, 0.375, 0.0), (0.7, 0.3, 0.0), (0.0, 0.3, 0.7)),
+    "protanopia": ((0.567, 0.433, 0.0), (0.558, 0.442, 0.0), (0.0, 0.242, 0.758)),
+    "tritanopia": ((0.95, 0.05, 0.0), (0.0, 0.433, 0.567), (0.0, 0.475, 0.525)),
+}
+
+
+def simulate(value: str, kind: str) -> str:
+    r, g, b = hex_to_rgb(value)
+    m = CVD_MATRICES[kind]
+    out = []
+    for row in m:
+        c = row[0] * r + row[1] * g + row[2] * b
+        out.append(max(0, min(255, round(c * 255))))
+    return "#{:02x}{:02x}{:02x}".format(*out)
+
+
+@dataclass(frozen=True)
+class Result:
+    ok: bool
+    detail: str
+
+
+def check(ramp: dict[str, str], *, floor: float = 20.0) -> list[Result]:
+    names = list(ramp)
+    results: list[Result] = []
+
+    # 1. pairwise separation, normal vision and each CVD type
+    for kind in ("normal", *CVD_MATRICES):
+        worst, pair = 999.0, ("", "")
+        for a, b in itertools.combinations(names, 2):
+            ca, cb = ramp[a], ramp[b]
+            if kind != "normal":
+                ca, cb = simulate(ca, kind), simulate(cb, kind)
+            d = delta_e(ca, cb)
+            if d < worst:
+                worst, pair = d, (a, b)
+        results.append(
+            Result(
+                worst >= floor,
+                f"{kind:<13} worst pair {pair[0]}/{pair[1]}: dE={worst:5.1f} "
+                f"(floor {floor})",
+            )
+        )
+
+    # 2. contrast against both theme backgrounds
+    for bg, label in (("#211d1b", "dark bg"), ("#f6f4f3", "light bg")):
+        worst, who = 99.0, ""
+        for name, value in ramp.items():
+            c = contrast(value, bg)
+            if c < worst:
+                worst, who = c, name
+        results.append(
+            Result(worst >= 3.0, f"{label:<13} worst {who}: {worst:4.2f}:1 (floor 3.0)")
+        )
+
+    # 3. monotonic lightness, so the ramp survives greyscale
+    lightness = [to_lab(v)[0] for v in ramp.values()]
+    mono = all(x > y for x, y in zip(lightness, lightness[1:])) or all(
+        x < y for x, y in zip(lightness, lightness[1:])
+    )
+    results.append(
+        Result(mono, "lightness     " + " ".join(f"{x:.0f}" for x in lightness))
+    )
+    return results
+
+
+if __name__ == "__main__":
+    import sys
+
+    # The shipped ramp (see ../tokens.md). Ordered by descending lightness so
+    # hue and lightness encode redundantly, which is what lets it carry an
+    # ordinal scale (grades A..F) as well as an unordered one.
+    RAMP = {
+        "cat-1": "#C57293",
+        "cat-2": "#398FC0",
+        "cat-3": "#C85A32",
+        "cat-4": "#228736",
+        "cat-5": "#8D58BB",
+        "cat-6": "#686D2C",
+    }
+    failures = 0
+    for r in check(RAMP):
+        print(("PASS " if r.ok else "FAIL ") + r.detail)
+        failures += not r.ok
+    print(f"\n{failures} failing check(s)")
+    sys.exit(1 if failures else 0)

unified-design-system/tokens.md

@@ -59,6 +59,53 @@ an image) — those stay `text-on-dark` (near-white), fixed regardless of
 page theme, since the scrim itself is always dark. `on-fill` only applies to
 the four *opaque* semantic fills above.
 
+## Categorical ramp
+
+For **charts, tags and category dots** — anything that needs N mutually
+distinguishable colours with no inherent meaning. Never for semantic state:
+success/warning/danger still own that, and mixing the two vocabularies is what
+makes a "red" category read as an error.
+
+| Token   | Hex       | L\* |
+| ------- | --------- | --- |
+| `cat-1` | `#C57293` | 58  |
+| `cat-2` | `#398FC0` | 56  |
+| `cat-3` | `#C85A32` | 52  |
+| `cat-4` | `#228736` | 49  |
+| `cat-5` | `#8D58BB` | 47  |
+| `cat-6` | `#686D2C` | 44  |
+
+**This ramp deliberately leaves the warm wedge**, and it is the only token group
+that does. Accent/success/warning/danger cluster in red-orange-yellow-olive and
+are separated mainly by lightness — a tradeoff that works when meaning carries
+the signal. A categorical ramp has no meaning to lean on, so hue separation *is*
+the requirement. Treating this as drift and "correcting" it back toward the
+wedge would destroy the only property it has.
+
+Chosen by search under four hard constraints, not by eye
+(`unified-design-system/scripts/ramp_check.py` re-runs the proof):
+
+1. **Pairwise CIE ΔE ≥ 20** between every pair — measured under normal vision
+   *and* simulated deuteranopia, protanopia and tritanopia. Worst observed: 34.6
+   normal, 26.0 deuteranopia, 25.6 protanopia, 27.4 tritanopia.
+2. **≥ 3:1 contrast against both backgrounds** (`ink` and `paper`), since the
+   ramp is theme-independent — it does not flip with `prefers-color-scheme`.
+   This is the binding constraint: colours legible on both a near-black and a
+   near-white field only exist in L\* ≈ 44–59, which is why the ramp is
+   mid-toned throughout rather than spanning light to dark.
+3. **Monotonically decreasing lightness** (58 → 44), so hue and lightness encode
+   redundantly. The ramp therefore still reads as an ordinal scale in greyscale
+   or under severe CVD, which is what lets `cat-1…6` carry an ordered scale
+   (grades A→F) as well as an unordered one.
+4. **Muted saturation**, to sit with the rest of the palette rather than
+   vibrating against it.
+
+Use them **in order** for ordered data, and *by position* for unordered data —
+never pick "the green one" because green means good, which is the semantic
+vocabulary leaking back in. Need a seventh category? That is a signal to group
+the tail into "other", not to extend the ramp: a 7th hue cannot clear ΔE 20
+against all six under CVD within the L\* 44–59 band.
+
 ## Spacing scale (4px base)
 
 `xs 4 · sm 8 · md 16 · lg 24 · xl 32 · xxl 48`
@@ -197,29 +244,6 @@ fully keyboard-operable. Making a gate keyboard-reachable is not weakening it.
 
 ## Screen size (required)
 
-| Target | Requirement |
-| ------ | ----------- |
-| **1366x768** | Fully usable. Nothing clipped, nothing unreachable. This is the primary machine. |
-| **1024x600** | Degrades gracefully — scrolls rather than clips. No hard minimum size above this. |
-
-Rules:
-
-1. **Budget the height, don't assume it.** 768px is the design target, not 1080.
-   Mixing a proportional content area with fixed chrome (`height = 0.7·H` above a
-   fixed-height button row) silently works at 1080 and fails at 768 — compute the
-   content budget as `available − measured chrome`.
-2. **Any view that can grow must scroll.** Lists, forms, anything whose height
-   depends on data (a day's log, an error string, accumulated history). An
-   unbounded error message is a real overflow source.
-3. **Never centre unscrollable content that can overflow.** A centre-anchored
-   container clips **symmetrically** when it is too tall — losing the header *and*
-   the submit button, with no scrollbar and no indication anything is missing.
-   Top-anchor it inside a scroll container instead.
-4. **Clamp width as well.** Prose stays at the 40rem/640px cap (rule 21) and
-   single-purpose inputs get a sensible max — a 4-digit number field stretched to
-   1334px is a violation even though nothing is clipped.
-5. **Don't let text scale break layout.** Rows that must not overflow use `Wrap`/
-   `Flexible` rather than a bare `Row`.
-
-`1366x768` and `1024x600` are landscape and *short*. Phone-portrait test sizes do
-not exercise either constraint, so both belong in the test matrix explicitly.
+Moved to `screen-size.md` (250-line cap): the 1366x768 / 1024x600 targets, the
+height-budgeting rules, and why centring unscrollable content clips
+symmetrically. Still part of this spec — read it for any layout work.

web_ui/README.md

@@ -13,7 +13,7 @@ this package is its executable form for the web.
 ```jsonc
 // package.json — pnpm only, see "Why the &path: suffix" below.
 "dependencies": {
-  "@kuhyx/web-ui": "github:kuhyx/utils#web_ui-v0.1.0&path:/web_ui"
+  "@kuhyx/web-ui": "github:kuhyx/utils#web_ui-v0.2.0&path:/web_ui"
 }
 ```
 
@@ -51,6 +51,21 @@ whose `dist/` is stale ships old code to every consumer with no error.
 | `quantile.ts` helpers | `nth`, `clamp01`, `quantileValue`, `valueQuantile`, `fractionFromPointer`. |
 | `fuzzyMatch` | Case-insensitive subsequence match. |
 
+### The categorical ramp
+
+`--cat-1` … `--cat-6` are for charts, tags and category dots — N mutually
+distinguishable colours with **no** inherent meaning. Never use them for
+semantic state; `--success`/`--warning`/`--danger` own that.
+
+They deliberately leave the warm wedge the rest of the palette sits in, because
+hue separation is the whole point of a categorical scale. The values were chosen
+by search under a ≥20 CIE ΔE floor across normal vision *and* deuteranopia,
+protanopia and tritanopia, ≥3:1 contrast on **both** backgrounds, and a
+monotonic lightness staircase so the ramp survives greyscale. Re-run the proof
+with `python3 ~/utils/unified-design-system/scripts/ramp_check.py` — it exits
+non-zero if an edit breaks any of it. A seventh hue is not available: the best
+candidate reaches only ΔE 17.9. Group the tail into "other" instead.
+
 `fractionFromPointer` is deliberately pure geometry: it makes the slider's
 behaviour testable without layout, which jsdom does not implement.
 

web_ui/dist/tokens.css

@@ -33,6 +33,27 @@
    * because the scrim itself is always dark. */
   --on-scrim: #eceae9;
 
+  /* Categorical ramp ------------------------------------------------------ */
+  /* For charts, tags and category dots — N mutually distinguishable colours
+   * with no inherent meaning. NEVER for semantic state; that stays
+   * success/warning/danger. Use them in ramp order for ordered data and by
+   * position for unordered data — never "the green one because green means
+   * good", which is the semantic vocabulary leaking back in.
+   *
+   * These deliberately leave the warm wedge every other token sits in: a
+   * categorical ramp has no meaning to lean on, so hue separation IS the
+   * requirement. Chosen by search under a >=20 CIE dE floor across normal
+   * vision and all three CVD types, >=3:1 on BOTH backgrounds, and a monotonic
+   * lightness staircase (58 -> 44) so the ramp survives greyscale. Do not edit
+   * a value here without re-running unified-design-system/scripts/ramp_check.py.
+   * They do not flip with prefers-color-scheme — they must hold on both. */
+  --cat-1: #c57293;
+  --cat-2: #398fc0;
+  --cat-3: #c85a32;
+  --cat-4: #228736;
+  --cat-5: #8d58bb;
+  --cat-6: #686d2c;
+
   /* Corner radius --------------------------------------------------------- */
   --radius-sm: 8px; /* buttons, inputs, chips */
   --radius-md: 12px; /* cards */

web_ui/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@kuhyx/web-ui",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "private": false,
   "type": "module",
   "description": "The shared token + component layer for kuhy's web apps: the frozen palette, spacing/radius/type scales as CSS custom properties, and the components that were each reimplemented in two or more repos.",

web_ui/src/test/setup.ts

@@ -1,38 +1,45 @@
 import "@testing-library/jest-dom/vitest";
 
+// Setup files run for every test file, including the ones that opt into the
+// node environment (tokens.test.ts reads CSS off disk). There is no DOM to
+// patch there, so bail out rather than throwing on a missing Element.
+const hasDom = typeof Element !== "undefined";
+
 // jsdom implements no layout engine (every rect is zero-sized) and no pointer
 // capture. The slider needs a non-zero track width for fractionFromPointer to
 // mean anything, and needs the capture calls to not throw.
 const TRACK_WIDTH = 1000;
 
-Object.defineProperty(Element.prototype, "getBoundingClientRect", {
-  configurable: true,
-  value(): DOMRect {
-    return {
-      bottom: 20,
-      height: 20,
-      left: 0,
-      right: TRACK_WIDTH,
-      toJSON: () => ({}),
-      top: 0,
-      width: TRACK_WIDTH,
-      x: 0,
-      y: 0,
-    };
-  },
-});
+if (hasDom) {
+  Object.defineProperty(Element.prototype, "getBoundingClientRect", {
+    configurable: true,
+    value(): DOMRect {
+      return {
+        bottom: 20,
+        height: 20,
+        left: 0,
+        right: TRACK_WIDTH,
+        toJSON: () => ({}),
+        top: 0,
+        width: TRACK_WIDTH,
+        x: 0,
+        y: 0,
+      };
+    },
+  });
 
-Object.defineProperties(Element.prototype, {
-  releasePointerCapture: {
-    configurable: true,
-    value: (): void => {
-      // No pointer capture in jsdom; the slider only needs the call to not throw.
+  Object.defineProperties(Element.prototype, {
+    releasePointerCapture: {
+      configurable: true,
+      value: (): void => {
+        // No pointer capture in jsdom; the slider only needs the call to not throw.
+      },
     },
-  },
-  setPointerCapture: {
-    configurable: true,
-    value: (): void => {
-      // As above.
+    setPointerCapture: {
+      configurable: true,
+      value: (): void => {
+        // As above.
+      },
     },
-  },
-});
+  });
+}

web_ui/src/tokens.css

@@ -33,6 +33,27 @@
    * because the scrim itself is always dark. */
   --on-scrim: #eceae9;
 
+  /* Categorical ramp ------------------------------------------------------ */
+  /* For charts, tags and category dots — N mutually distinguishable colours
+   * with no inherent meaning. NEVER for semantic state; that stays
+   * success/warning/danger. Use them in ramp order for ordered data and by
+   * position for unordered data — never "the green one because green means
+   * good", which is the semantic vocabulary leaking back in.
+   *
+   * These deliberately leave the warm wedge every other token sits in: a
+   * categorical ramp has no meaning to lean on, so hue separation IS the
+   * requirement. Chosen by search under a >=20 CIE dE floor across normal
+   * vision and all three CVD types, >=3:1 on BOTH backgrounds, and a monotonic
+   * lightness staircase (58 -> 44) so the ramp survives greyscale. Do not edit
+   * a value here without re-running unified-design-system/scripts/ramp_check.py.
+   * They do not flip with prefers-color-scheme — they must hold on both. */
+  --cat-1: #c57293;
+  --cat-2: #398fc0;
+  --cat-3: #c85a32;
+  --cat-4: #228736;
+  --cat-5: #8d58bb;
+  --cat-6: #686d2c;
+
   /* Corner radius --------------------------------------------------------- */
   --radius-sm: 8px; /* buttons, inputs, chips */
   --radius-md: 12px; /* cards */

web_ui/src/tokens.test.ts

@@ -0,0 +1,111 @@
+// @vitest-environment node
+import { readFileSync } from "node:fs";
+
+import { describe, expect, it } from "vitest";
+
+const css = readFileSync(new URL("tokens.css", import.meta.url), "utf8");
+
+/**
+ * tokens.css is the executable form of unified-design-system/tokens.md. These
+ * assertions are the gate against silent drift between the two: the palette is
+ * frozen, so a changed hex here is either a deliberate design-system change
+ * (update both, plus the Dart side) or a bug.
+ */
+
+function declared(name: string): string[] {
+  return [...css.matchAll(new RegExp(`--${name}:\\s*([^;]+);`, "g"))].map((m) =>
+    (m[1] ?? "").trim(),
+  );
+}
+
+describe("tokens.css", () => {
+  it.each([
+    ["bg", "#211d1b"],
+    ["surface-1", "#2b2624"],
+    ["surface-2", "#38312e"],
+    ["border", "#463e3a"],
+    ["text", "#eceae9"],
+    ["text-muted", "#aaa09a"],
+    ["accent", "#b8862e"],
+    ["success", "#8a9a3c"],
+    ["warning", "#e0a63c"],
+    ["danger", "#e2585f"],
+  ])("declares --%s with the frozen dark value first", (name, value) => {
+    expect(declared(name)[0]).toBe(value);
+  });
+
+  it.each([
+    ["bg", "#f6f4f3"],
+    ["surface-1", "#fcfbfb"],
+    ["border", "#e0dad7"],
+    ["text", "#211d1b"],
+    ["text-muted", "#70625b"],
+  ])("overrides --%s for the light theme", (name, value) => {
+    expect(declared(name)).toContain(value);
+  });
+
+  it("keeps on-fill dark, never near-white", () => {
+    // Every semantic fill sits in the same mid-light band, where near-white
+    // text measures 2.2:1-3.6:1 against a 4.5:1 floor.
+    expect(declared("on-fill")).toEqual(["#211d1b"]);
+  });
+
+  it("keeps on-scrim fixed regardless of page theme", () => {
+    expect(declared("on-scrim")).toEqual(["#eceae9"]);
+  });
+
+  it("ships the full categorical ramp", () => {
+    expect([1, 2, 3, 4, 5, 6].map((n) => declared(`cat-${String(n)}`)[0])).toEqual([
+      "#c57293",
+      "#398fc0",
+      "#c85a32",
+      "#228736",
+      "#8d58bb",
+      "#686d2c",
+    ]);
+  });
+
+  it("does not re-theme the categorical ramp", () => {
+    // The ramp must hold on both backgrounds rather than flipping with the
+    // page theme; a second declaration would mean someone themed it.
+    for (const n of [1, 2, 3, 4, 5, 6]) {
+      expect(declared(`cat-${String(n)}`)).toHaveLength(1);
+    }
+  });
+
+  it("declares the spacing scale on the 4px base", () => {
+    expect([1, 2, 3, 4, 5, 6].map((n) => declared(`space-${String(n)}`)[0])).toEqual([
+      "4px",
+      "8px",
+      "16px",
+      "24px",
+      "32px",
+      "48px",
+    ]);
+  });
+
+  it("declares the radius scale", () => {
+    expect(["sm", "md", "lg"].map((s) => declared(`radius-${s}`)[0])).toEqual([
+      "8px",
+      "12px",
+      "16px",
+    ]);
+  });
+
+  it("declares the type scale", () => {
+    expect(
+      ["display", "title", "subtitle", "body", "label", "caption"].map(
+        (s) => declared(`text-${s}`)[0],
+      ),
+    ).toEqual(["32px", "24px", "20px", "16px", "14px", "12px"]);
+  });
+
+  it("styles :focus-visible, so no consumer has to remember to", () => {
+    expect(css).toMatch(/:focus-visible\s*\{[^}]*outline:\s*2px solid var\(--focus-ring\)/);
+  });
+
+  it("uses no raw black or white literals", () => {
+    // Shadows are ink-tinted rgba; neutrals are never pure.
+    expect(css).not.toMatch(/#fff\b|#ffffff\b|#000\b|#000000\b|rgba\(0,\s*0,\s*0/i);
+  });
+});