Color Accessibility

Prove every fg/bg pair with math before shipping colors. pastel has no contrast subcommand — use main.py in this skill directory for ratios; use pastel for manipulation (textcolor, mix, darken, lighten, format).

When to use / not use

• Use: contrast checks, picking text on a fill, fixing failing pairs, dimmed/inactive text, theme palette audit.
• Do not use: brand-only palette vibes with no readability ask; full diagram authoring (use diagram — it has its own contrast step).

Work phases in order. Do not skip. Do not invent ratios from memory.

Prerequisites

pastel --version    # required on PATH
python3 color-accessibility/main.py --help

If pastel is missing: tell the user to install (brew install pastel or cargo install pastel) and STOP.

Resolve main.py relative to this skill directory (or the path you loaded the skill from).

Thresholds (default)

Deeper WCAG notes: load references/wcag.md only if large-text, non-text UI, or AAA is disputed.

Phase 1 — Capture pairs

1. List every fg/bg (or fill/font-color) pair the user cares about as hex or named colors.
2. Completion: each pair has explicit fg and bg strings (no "something light gray").

Phase 2 — Measure (required)

For each pair:

python3 main.py contrast --fg '<fg>' --bg '<bg>'
# large text:
python3 main.py contrast --fg '<fg>' --bg '<bg>' --large-text

• Exit 0 + "status":"success" -> meets default min.
• Exit 1 + "status":"fail" -> record ratio and continue to Phase 3.
• "status":"error" -> report reason and STOP (or fix input colors).

Optimal black/white fg for a background only:

python3 main.py textcolor --bg '<bg>'
# equivalent core: pastel textcolor '<bg>' | pastel format hex

Completion: every pair has a JSON result with ratio, level, passes_aa.

Phase 3 — Fix failures

Do not hand-pick hex. Prefer:

python3 main.py fix --fg '<fg>' --bg '<bg>' --adjust auto --min-ratio 4.5

• auto: try pastel textcolor on bg first; else nudge fg lightness.
• Prefer the textcolor / high-ratio result (often black or white, frequently AAA). Do not scrape the nearest gray that barely clears 4.5:1 unless the user asked to preserve a gray look.
• --adjust fg|bg when the user freezes one side.
• Re-run contrast on the returned pair.fg / pair.bg.

Manual pastel knobs (when fix is wrong for the aesthetic):

pastel darken 0.1 '<color>' | pastel format hex
pastel lighten 0.15 '<color>' | pastel format hex
pastel desaturate 0.2 '<color>' | pastel format hex

Completion: every required pair passes_aa (or user explicitly accepted a documented exception).

Phase 4 — Dimmed / mixed roles

Inactive text = mix fg toward bg in a perceptual space (default Lab):

python3 main.py mix-dim --fg '<active_fg>' --bg '<bg>' --fraction 0.6
# fraction = pastel --fraction = how much of the *base fg* is kept (0-1)

Then contrast the mixed color vs bg. If < 3:1, raise --fraction (keep more fg) or fix via Phase 3.

Completion: dim color hex + ratio; dim ratio < active ratio when both exist.

Phase 5 — Deliver

1. Emit final hex pairs (and ratios) in the user's target format (CSS, Lua hl, JSON, table).
2. Cite measured ratios next to each pair (e.g. 12.8:1 AAA).
3. Never claim WCAG pass without a Phase 2 (or post-fix) main.py result in this turn.

Completion: user-ready snippet + no unverified pairs.

Commands cheat sheet

Edge cases

• Transparent / alpha: flatten onto the real background first; do not contrast alpha hex alone.
• Gradient text: check against the lightest and darkest stops under the glyphs.
• Syntax themes: active vs comment/dimmed both need Phase 2; comments still >= 3:1.
• diagram skill: for D2 class fills, diagram/main.py check-contrast is enough inside diagram work.

Non-examples (do not load this skill alone)

• "Draw a C4 diagram of our services" -> diagram
• "What is the complementary hue of blue?" -> plain pastel complement is enough unless readability is in scope