algorithmic-color-palette

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SKILL.md

---
name: algorithmic-color-palette
description: Derive a full UI palette from one or two brand colours — state variants, brand-tinted greys, semantic colours. Use when building or expanding a colour system.
metadata:
  priority: 8
  pathPatterns:
    - "**/*.css"
    - "**/*.scss"
    - "**/tokens/**"
    - "**/theme/**"
    - "tailwind.config.*"
    - "design-system/**"
  promptSignals:
    phrases:
      - "colour palette"
      - "color palette"
      - "brand colours"
      - "derive colours"
      - "colour tokens"
      - "hover colour"
      - "shade"
      - "tint"
      - "colour system"
  retrieval:
    aliases:
      - colour system
      - algorithmic colours
      - brand colour palette
      - derive shades
      - colour tokens
    intents:
      - generate a colour palette from brand colours
      - derive hover and active colours
      - create grey palette from brand
      - build a full colour system
      - extend a limited brand palette
    examples:
      - generate a full colour palette from this brand blue
      - what colour should the hover state be
      - create a grey palette that fits this brand
      - derive semantic colours from the brand primary
---

# Algorithmic Colour Palette

A brand palette of 2–3 colours is not enough for a UI. You need shades for states (hover, active, disabled), neutrals for backgrounds and borders, and semantic colours for status. Deriving these algorithmically from the brand colours produces a palette that feels coherent — everything is visually related to the brand rather than pulled from a generic grey or a stock colour library.

> **Don't guess the seed colours — extract them (dembrandt engine, optional).** If the brand already exists on the web, pull its *real* palette off the live site instead of eyeballing a hex: `get_color_palette` (or the `extract-design` skill) returns the actual computed brand and neutral colours from the DOM, which you then expand with the methods below. See [`extract-design`](../extract-design/SKILL.md) for setup.

## Deriving Interactive State Colours

From each brand colour, generate at minimum three variants: base, darker (hover/active), lighter (tint/background).

### Method: HSL adjustment

```
base:    hsl(H, S%, L%)
hover:   hsl(H, S%, L% - 8%)     ← darken by reducing lightness
active:  hsl(H, S%, L% - 14%)    ← darken further
tint:    hsl(H, S%, L% + 40%)    ← lighten significantly for backgrounds
subtle:  hsl(H, S% * 0.3, L% + 45%)  ← heavily desaturated, near-white
```

### Example: brand primary `#133174` (hsl 224, 70%, 27%)

```css
--color-primary-subtle:  hsl(224, 21%, 94%);  /* background tint */
--color-primary-tint:    hsl(224, 70%, 67%);  /* light variant */
--color-primary:         hsl(224, 70%, 27%);  /* base */
--color-primary-hover:   hsl(224, 70%, 19%);  /* hover: -8% lightness */
--color-primary-active:  hsl(224, 70%, 13%);  /* active: -14% lightness */
```

### Example: success green derived from a teal brand colour

If the brand has a green or teal, shift it toward a clearer success green:

```css
--color-success-subtle:  hsl(142, 20%, 94%);
--color-success:         hsl(142, 60%, 35%);
--color-success-hover:   hsl(142, 60%, 27%);
```

## Deriving Brand-Tinted Greys

Generic greys (`#666`, `#999`, `#eee`) feel disconnected from the brand. Desaturating the brand hue produces greys that are subtly tinted — warm, cool, or neutral depending on the brand — and feel like they belong to the same palette.

### Optical Comfort: Avoiding Pure Black on White
Pure black `#000000` on pure white `#FFFFFF` causes halation and eye strain. Use a near-black such as `#222222` (`grey-900`) for text and an off-white such as `#EEEEEE` (`grey-50`) for backgrounds; the softened pair still passes WCAG AA/AAA and reads as less harsh.

### Publish Roles, Not Only Swatches
Named chips with hex values are not a system until each colour has a role: surface, surface tint, text, link, accent, decoration. Name the humble roles too, the off-white behind cards, stripes and hairlines. A role left unnamed is filled by a framework default, which is how an off-brand neutral ends up painting most of the pixels. Two teams inventing the same missing tint with different values means a role is missing, not a colour.

### Method: desaturate + adjust lightness

```
brand hue H
grey-900: hsl(H, 12%, 10%)   ← near-black, text
grey-700: hsl(H, 10%, 30%)   ← dark text, icons
grey-500: hsl(H,  8%, 50%)   ← secondary text, placeholders
grey-300: hsl(H,  6%, 70%)   ← disabled text, subtle labels
grey-200: hsl(H,  5%, 82%)   ← borders, dividers
grey-100: hsl(H,  4%, 92%)   ← input backgrounds, table stripes
grey-50:  hsl(H,  3%, 96%)   ← page background, subtle fills
```

### Example: brand primary `#133174` (H = 224, blue-tinted)

```css
--color-grey-900: hsl(224, 12%, 10%);  /* #16171f — slightly blue-black */
--color-grey-500: hsl(224,  8%, 50%);  /* #7b7e8a — cool grey */
--color-grey-200: hsl(224,  5%, 82%);  /* #cfd0d5 — cool light border */
--color-grey-50:  hsl(224,  3%, 96%);  /* #f4f4f6 — near-white with a hint of blue */
```

Compare to generic `#f5f5f5` (no hue) — the brand-tinted version is subtly different but feels intentional.

## Semantic Colour Derivation

Status colours (error, warning, success, info) should feel harmonious with the brand. To achieve cohesion, align their **Saturation** and **Lightness** to create a consistent "visual weight" across the status set.

### Method: Aligned visual weight

1. **Pick the Hues:** Use standard semantic hues (0 for Error, 38 for Warning, 142 for Success).
2. **Align S & L:** Use the saturation and lightness of your Brand Primary as a starting point.
3. **Adjust for Perceived Brightness:** Hues like Yellow/Orange (Warning) feel brighter than Blue/Red. Reduce the lightness of Warning by 5–10% compared to Success or Error to ensure they feel equally "heavy" on the page.

| Semantic | Hue (H) | Saturation (S) | Lightness (L) |
|---|---|---|---|
| **Error** | 0–10 | Match Primary | Match Primary |
| **Warning** | 35–45 | Match Primary | Primary L - 10% |
| **Success** | 140–160 | Match Primary | Match Primary |
| **Info** | 210–230 | Match Primary | Match Primary |

**The "Vibrancy" Rule:** If the brand is muted (low saturation), the semantic colours should also be slightly muted. If the brand is neon/vibrant, the semantics should follow suit. Cohesion comes from shared intensity.

## Functional and Interactive Colours

Standard UI elements require dedicated functional tokens beyond basic brand and semantic colours.

### Focus States
Focus indicators are critical for accessibility. Use a high-visibility colour that works on all backgrounds.
- **Default:** Brand Primary (if contrast is high enough).
- **Fallback:** A dedicated high-contrast blue `hsl(215, 95%, 50%)`.
- **Token:** `--color-focus`.

### Selection and Highlights
Text selection and list item highlights should be subtle and non-distracting.
- **Method:** Use the primary hue with very high lightness (90%+) and moderate saturation.
- **Token:** `--color-selection`.

### Overlays and Modals
Backdrops for modals or drawers need a neutral, semi-transparent colour.
- **Method:** Use your `grey-900` hue with an alpha channel.
- **Token:** `--color-overlay: hsla(H, 12%, 10%, 0.5);`

### Skeleton and Loading
Loading states should be neutral and recessive.
- **Method:** Use `grey-200` as the base and `grey-100` as the shimmer highlight.
- **Token:** `--color-skeleton`.

### Disabled States
Disabled elements must communicate unreachability.
- **Method:** Use `grey-500` for text and `grey-200` for backgrounds/borders.
- **Rule:** Avoid using brand tints for disabled backgrounds to prevent "pseudo-active" confusion.

### Brand-Tinted Shadows
Premium UIs avoid pure black shadows. Use a very dark, desaturated brand hue.
- **Method:** `hsla(H, 15%, 5%, alpha)` where H is the brand hue.
- **Token:** `--color-shadow-base`.

### Links
- **Base:** Brand Primary or a dedicated high-visibility blue.
- **Visited:** Shift primary hue toward purple (+20) and reduce saturation.
- **Token:** `--color-link`, `--color-link-visited`.

### Input and Validation
- **Method:** Use semantic base colours for borders and text in error/success states.
- **Inactive Border:** `grey-200`.
- **Active/Focus Border:** Brand Primary.

## Full Token Output Example

```css
:root {
  /* Primary — derived from brand #133174 */
  --color-primary-subtle:  hsl(224, 21%, 94%);
  --color-primary-tint:    hsl(224, 70%, 67%);
  --color-primary:         hsl(224, 70%, 27%);
  --color-primary-hover:   hsl(224, 70%, 19%);
  --color-primary-active:  hsl(224, 70%, 13%);

  /* Brand-tinted neutrals */
  --color-grey-900: hsl(224, 12%, 10%);
  --color-grey-700: hsl(224, 10%, 30%);
  --color-grey-500: hsl(224,  8%, 50%);
  --color-grey-300: hsl(224,  6%, 70%);
  --color-grey-200: hsl(224,  5%, 82%);
  --color-grey-100: hsl(224,  4%, 92%);
  --color-grey-50:  hsl(224,  3%, 96%);

  /* Semantic */
  --color-error:   hsl(4,  72%, 44%);
  --color-warning: hsl(38, 80%, 44%);
  --color-success: hsl(142, 58%, 35%);
  --color-info:    hsl(224, 70%, 27%); /* = primary */

  /* Semantic subtle backgrounds */
  --color-error-subtle:   hsl(4,  50%, 95%);
  --color-warning-subtle: hsl(38, 60%, 95%);
  --color-success-subtle: hsl(142, 40%, 95%);

  /* Functional */
  --color-focus:     var(--color-primary);
  --color-selection: hsl(224, 70%, 90%);
  --color-overlay:   hsla(224, 12%, 10%, 0.5);
  --color-skeleton:  var(--color-grey-200);
  --color-shadow:    hsla(224, 15%, 5%, 0.1);

  /* Links */
  --color-link:         var(--color-primary);
  --color-link-visited: hsl(244, 40%, 35%);
}
```

## Review Checklist

- [ ] Are hover and active colours derived from the base by lightness adjustment, not chosen independently?
- [ ] Are neutral greys tinted with the brand hue rather than using generic `#666` / `#eee`?
- [ ] Is saturation reduced progressively as lightness increases in the grey scale?
- [ ] Is pure black (#000000) on pure white (#FFFFFF) avoided in favor of near-blacks (e.g., #222) and off-whites (e.g., #EEE)?
- [ ] Are status colours (Success, Warning, Error) visually weighted to match the brand primary?
- [ ] If the brand primary is orange or amber, is warning colour clearly distinct from it?
- [ ] Does each brand colour have at minimum: subtle, base, hover, active variants?
- [ ] Does every colour carry a role (surface, text, link, accent), including the off-white for cards and hairlines?
- [ ] Are semantic colours aligned in Saturation and Lightness to create a cohesive visual weight?
- [ ] Is there a dedicated `--color-focus` token that meets accessibility contrast requirements?
- [ ] Are selection, overlay, and shadow colours derived from the brand hue rather than generic black/grey?
- [ ] Are disabled states neutral (greys) to avoid confusion with interactive brand colours?
- [ ] Does the link colour have a distinct `visited` state derived algorithmically?

## Common Anti-Patterns

| Anti-pattern | Problem | Fix |
|---|---|---|
| **Pure black on pure white** | High visual strain, "halation" | Use near-black (#222) and off-white (#EEE) |
| **Grey borders next to colourful areas** | Looks cheap and disconnected | Remove border or use a tinted/darker version of the adjacent colour |
| **Randomly picked "Warning/Error" colours** | Palette feels uncoordinated | Derive from brand HSL with visual weight alignment |
| **Generic grey palette (#666, #999)** | Lacks brand identity | Tint neutrals with a low-saturation version of the brand hue |