/algorithmic-color-palette

name: algorithmic-color-palette
description: Derive a full UI colour palette algorithmically from one or two brand colours. Darker and lighter variants for interactive states, desaturated greys from the brand hue for borders and backgrounds, and semantic colours that feel coherent with the brand rather than generic. Use when building a colour system from scratch or expanding a limited brand palette for UI use.
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%)

--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:

--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

Extreme contrast (pure black `#000000` on pure white `#FFFFFF`) can cause "halation" and eye strain. To create a more comfortable reading experience:

• **Use "Near-Black" for text:** Use a very dark grey (e.g., `#222222` or your `grey-900` token) instead of pure black.
• **Use "Off-White" for backgrounds:** A slightly muted white (e.g., `#EEEEEE` or your `grey-50` token) is softer on the eyes than pure `#FFFFFF`.

This "softened contrast" remains highly accessible (passing WCAG AA/AAA) but feels more professional and less harsh.

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)

--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 | M