docs: add comprehensive guide to color scales and contrast patterns

.github/workflows/ci.yml

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     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Set up Node.js
         uses: actions/setup-node@v4

.husky/pre-commit

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+npx tsx scripts/checkRemovedTokens.ts --base HEAD

COLOR_SCALES.md

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+# Color Scales in Primer Design Tokens
+
+This document explains how color scales work in primer/primitives, how they're structured, and the constraints that guide them.
+
+## Overview
+
+Primer's color system is built on **base color scales** — semantic palettes (neutral, blue, green, red, etc.) that serve as the foundation for **functional tokens** (fgColor, bgColor, borderColor, etc.).
+
+- **Base scales:** Raw color values organized by hue and lightness step
+- **Functional tokens:** Semantic aliases that layer contrast requirements, accessibility rules, and theme-aware logic on top of base scales
+- **Themes:** Light, dark, dark-dimmed, high-contrast variants that reuse the same functional token names with different values
+
+## Base Color Scales
+
+### Scale Structure
+
+Each base scale has **13 steps** (0–13):
+
+| Step | Purpose | Light Theme (neutral example) |
+|------|---------|-------------------------------|
+| 0 | **Brightest/Lightest** | `#ffffff` (white) |
+| 1–7 | **Light backgrounds** | `#f6f8fa` → `#c8d1da` (gradual darkening) |
+| 8–11 | **Text & borders** | `#818b98` → `#393f46` (medium to dark gray) |
+| 12–13 | **Darkest/Highest contrast** | `#25292e` → `#1f2328` (black) |
+
+**Why 13 steps?** They provide:
+- Enough granularity for fine contrast control (especially in mid-tones, steps 5–8)
+- Semantic meaning tied to use cases (light backgrounds, text, borders)
+- Predictable progression for interpolation and theme adaptation
+
+### Current Scales
+
+Primer defines base scales for:
+- **Neutral** (gray, used for defaults, text, borders)
+- **Blue** (primary accent color)
+- **Green** (success)
+- **Red** (danger)
+- **Yellow** (warning)
+- **Purple** (emphasis)
+- Plus specialized scales: orange, pink, coral, lime, cyan, indigo
+
+### Scale Files
+
+All base scales are defined in JSON5 files:
+
+```
+src/tokens/base/color/
+├── light/
+│   ├── light.json5              # Base light theme (default 0-13 steps)
+│   ├── light.high-contrast.json5
+│   ├── display-light.json5      # Display color scales (accent colors)
+├── dark/
+│   ├── dark.json5
+│   ├── dark.dimmed.json5
+│   ├── dark.high-contrast.json5
+│   └── display-dark.json5
+```
+
+## Functional Tokens Layer
+
+### Why Functional Tokens Exist
+
+**Problem:** If consumers directly used base scales, they'd have to:
+- Know which step is safe for text on which background
+- Remember which step means "hover" vs. "active"
+- Rewrite logic for each new theme
+
+**Solution:** Functional tokens abstract this complexity:
+
+```json5
+// Bad: consumer has to think about steps
+color: $base.color.neutral.5   // Is this readable on neutral.0? Need to check contrast
+
+// Good: semantic name, works across all themes
+color: $base.color.fgColor.default  // Guaranteed to meet 4.5:1 contrast on default bg
+```
+
+### Examples of Functional Tokens
+
+| Token | Purpose | Light Value | Dark Value |
+|-------|---------|-------------|-----------|
+| `fgColor.default` | Main text | `neutral.12` | `neutral.1` |
+| `fgColor.muted` | Secondary text (lower contrast) | `neutral.8` | `neutral.4` |
+| `bgColor.default` | Main background | `neutral.0` | `neutral.13` |
+| `bgColor.emphasis` | Highlighted background | `blue.1` | `blue.9` |
+| `borderColor.default` | Standard border | `neutral.6` | `neutral.7` |
+
+### Functional Token Structure
+
+Functional tokens live in:
+
+```
+src/tokens/functional/
+├── color/
+│   ├── fgColor.json5
+│   ├── bgColor.json5
+│   ├── borderColor.json5
+│   ├── control.json5            # Buttons, inputs, selects
+│   ├── button.json5
+│   ├── avatar.json5
+│   ├── counter.json5
+│   └── [100+ more specialized tokens]
+```
+
+Each functional token file references base scales:
+
+```json5
+{
+  fgColor: {
+    default: {
+      $value: '{base.color.neutral.12}',  // ← References step 12 of neutral scale
+      $type: 'color'
+    },
+    muted: {
+      $value: '{base.color.neutral.8}',   // ← Step 8 for lower contrast
+      $type: 'color'
+    }
+  }
+}
+```
+
+**Theme-aware behavior:**
+The same `fgColor.default` token can resolve to different values in light vs. dark themes by updating the reference:
+
+```json5
+// light.json5
+fgColor.default: '{base.color.neutral.12}'   // Dark text on light bg
+
+// dark.json5  
+fgColor.default: '{base.color.neutral.1}'    // Light text on dark bg
+```
+
+## Contrast Requirements
+
+Primer enforces [WCAG 2.1 AA compliance](https://www.w3.org/TR/WCAG21/) via documented contrast rules:
+
+### Text Contrast
+
+| Pair | Ratio | Rule |
+|------|-------|------|
+| Text vs. background | **4.5:1** | Required for all text |
+| Links vs. surrounding text | **3:1** | In addition to 4.5:1 against bg |
+| Placeholder text vs. bg | **4.5:1** | Or use visible label |
+| Disabled text | None | No requirement |
+
+### Non-Text Contrast
+
+| Pair | Ratio | Rule |
+|------|-------|------|
+| Focus border vs. adjacent colors | **3:1** | Outline around interactive controls |
+| Empty control border vs. bg | **3:1** | Unfilled buttons, empty inputs |
+| States shown together | **3:1** | Selected vs. unselected in segmented controls |
+| Decorative elements | None | No requirement |
+
+### Contrast Checking
+
+Primer runs automated contrast checks via `scripts/colorContrast.ts`:
+
+```bash
+npm run build:tokens          # Generates all token files
+npm run check:contrast        # Runs contrast test
+```
+
+**Output:** `color-contrast-check.json` lists all failed pairs with:
+- Actual contrast ratio
+- Required ratio
+- Which colors failed
+- Specific theme/context
+
+**Example violation:**
+```json
+{
+  "contrastPair": "fgColor.muted vs. bgColor.default",
+  "pass": "❌",
+  "contrastRatio": "3.8:1",
+  "minimumContrastRatio": "4.5:1",
+  "theme": "light"
+}
+```
+
+## How Changes Propagate
+
+### Scenario: Update neutral scale (like PR #1340)
+
+1. **Change base scale** (light.json5, dark.json5, etc.):
+   ```json5
+   neutral: {
+     5: { $value: '#new-hex' }  // ← Old hex was #old-hex
+   }
+   ```
+
+2. **Functional tokens automatically updated:**
+   - Any token referencing `{base.color.neutral.5}` now uses the new hex
+   - No manual edits needed for those references
+
+3. **But:** If the new hex breaks contrast, we have two options:
+   - **Option A:** Bump the reference to a darker step
+     ```json5
+     fgColor.muted: '{base.color.neutral.9}'  // Changed from neutral.8
+     ```
+     → This cascades: any reference to `neutral.8` must be updated
+
+   - **Option B:** Add new steps to preserve old semantic meaning
+     ```json5
+     neutral: {
+       14: { $value: '#new-light-variant' },
+       15: { $value: '#new-lighter-variant' }
+     }
+     ```
+     → Fewer cascading changes, but more scale maintenance
+
+### Current Problem (PR #1340)
+
+Shifting base `neutral` from blue-gray to green-gray:
+- Some old steps need to shift `+1` positions (old step 6 → new step 7)
+- Other steps need `+2` (old step 5 → new step 7, too)
+- **Non-uniform mapping** → ~1,800 manual reference updates across functional tokens
+
+**Why this happens:**
+- Step progression isn't linear (lightness gaps vary)
+- Color shift (blue → green) changes perceptual intensity
+- Can't reliably map old steps to new steps without contrast checking each one
+
+## Best Practices for Scale Changes
+
+1. **Preserve step semantics:** If you change a scale, keep the same step doing roughly the same job (e.g., step 6 should still be "medium gray suitable for borders")
+
+2. **Extend if needed:** Rather than reordering, add steps (14, 15, 16, etc.) to absorb changes without fracturing existing references
+
+3. **Test contrast holistically:** After any change, run the contrast script and review all failures together—don't fix them ad-hoc
+
+4. **Document mapping:** If you do change step meanings, create a migration guide showing old→new references
+
+5. **Consider functional token impact:** Count the cascading reference changes before committing to a scale change
+
+## Themes
+
+Primer currently has **8 color modes:**
+
+| Name | Purpose | Base Scales |
+|------|---------|-------------|
+| `light` (default) | Standard light mode | 13 steps per scale |
+| `dark` | Standard dark mode | 13 steps per scale |
+| `dark-dimmed` | Reduced contrast dark mode | 13 steps per scale |
+| `light-high-contrast` | WCAG AAA (7:1) for light | 13 steps per scale |
+| `dark-high-contrast` | WCAG AAA (7:1) for dark | 13 steps per scale |
+| `dark-colorblind-high-contrast` | Protanopia-friendly HC dark | 13 steps per scale |
+| `light-tritanopia-high-contrast` | Tritanopia-friendly HC light | 13 steps per scale |
+| Display themes | Accent color scales only | Same 13 steps |
+
+Each theme is built from the same **functional token definitions**, but with different base scale values.
+
+## Key Files
+
+| File | Purpose |
+|------|---------|
+| `src/tokens/base/color/light/light.json5` | Base scales for light mode (source of truth) |
+| `src/tokens/functional/color/fgColor.json5` | Text color token definitions |
+| `src/tokens/functional/color/bgColor.json5` | Background color tokens |
+| `scripts/colorContrast.ts` | Contrast checker |
+| `scripts/colorContrast.config.ts` | Contrast requirements (4.5:1, 3:1, etc.) |
+| `contributor-docs/adrs/adr-010-color-contrast.md` | Design rationale for contrast rules |
+
+## Questions?
+
+- **Why base scales?** Provide reusable, predictable primitives
+- **Why 13 steps?** Balance between granularity and semantic clarity
+- **Why functional tokens?** Hide complexity, ensure accessibility, enable themes
+- **Why enforce contrast?** Legal requirement (WCAG 2.1) + ethical duty (accessibility)
+
+---
+
+**Version:** April 2026  
+**Author:** Primer Design Systems team

contributor-docs/agents/token-authoring.md

@@ -90,3 +90,42 @@ Add `org.primer.llm` to include tokens in `DESIGN_TOKENS_SPEC.md`:
 4. Add `org.primer.llm` if it should appear in LLM guidelines
 
 5. Run: `npm run lint && npm run test && npm run build`
+
+## Removing or Renaming Tokens
+
+When you remove or rename tokens in `src/tokens/`, you **must** document them in `src/tokens/removed/removed.json`.
+
+### File format
+
+`src/tokens/removed/removed.json` is a flat JSON object. Each key is the source token path (dot-separated, matching the nested key structure in the JSON5 source files). The value is either:
+
+- `null` — token was fully deleted with no replacement
+- `"new.token.path"` — token was renamed/replaced (points to the new name)
+
+### Example
+
+If you removed `fgColor.onInverse` and renamed `bgColor.accent` → `bgColor.accent.default`, add:
+
+```json
+{
+  "fgColor.onInverse": null,
+  "bgColor.accent": "bgColor.accent.default"
+}
+```
+
+### How to derive the token path
+
+Token paths come from the nested keys in the JSON5 source files, joined with `.`. For example, this token in `src/tokens/functional/color/fgColor.json5`:
+
+```json5
+{fgColor: {muted: {$value: '...', $type: 'color'}}}
+```
+
+has the path `fgColor.muted`. The file name/location does not matter — only the nested object keys matter.
+
+### Rules
+
+1. Create `src/tokens/removed/removed.json` if it doesn't exist
+2. If it already exists, merge your entries into it (don't overwrite existing entries)
+3. Every token path you delete or rename must have an entry
+4. Use `null` for deletions, use the new token path string for renames