curiositech/color-contrast-auditor

Color Contrast Auditor

Detects color contrast violations that make text unreadable and provides WCAG-compliant fixes. Uses both mathematical contrast ratio analysis and perceptual evaluation via vision capabilities.

When to Use

Activate on:

• Screenshots of websites/apps with suspected contrast issues
• CSS/Tailwind files for color audit
• "I can't read this" or "this is hard to see"
• Pre-launch accessibility checks
• Design system color validation

NOT for:

• Choosing brand colors (use web-design-expert)
• Color harmony/aesthetics (use color-theory-palette-harmony-expert)
• Non-visual accessibility (screen readers, keyboard nav)

---

WCAG 2.1 Contrast Requirements

Minimum Ratios (AA - Required)

| Text Type | Minimum Ratio | Example | |-----------|---------------|---------| | Normal text (<24px, <18.66px bold) | 4.5:1 | Body copy, labels, buttons | | Large text (≥24px or ≥18.66px bold) | 3:1 | Headlines, hero text | | UI components (borders, icons) | 3:1 | Form inputs, icons, focus rings | | Graphical objects | 3:1 | Charts, infographics |

Enhanced Ratios (AAA - Recommended)

| Text Type | Minimum Ratio | |-----------|---------------| | Normal text | 7:1 | | Large text | 4.5:1 |

Non-Text Elements

| Element | Requirement | |---------|-------------| | Focus indicators | 3:1 against adjacent colors | | Form field borders | 3:1 against background | | Icons conveying meaning | 3:1 against background | | Disabled elements | No requirement (but consider UX) |

---

Contrast Ratio Formula

Contrast Ratio = (L1 + 0.05) / (L2 + 0.05)

Where L1 = lighter color's relative luminance
      L2 = darker color's relative luminance

Calculating Relative Luminance

function relativeLuminance(r, g, b) {
  // Convert 0-255 to 0-1
  let [rs, gs, bs] = [r, g, b].map(c => c / 255);

  // Apply gamma correction
  const gamma = c => c <= 0.03928
    ? c / 12.92
    : Math.pow((c + 0.055) / 1.055, 2.4);

  const [R, G, B] = [rs, gs, bs].map(gamma);

  // Weighted sum (human eye sensitivity)
  return 0.2126 * R + 0.7152 * G + 0.0722 * B;
}

function contrastRatio(color1, color2) {
  const l1 = relativeLuminance(...color1);
  const l2 = relativeLuminance(...color2);
  const lighter = Math.max(l1, l2);
  const darker = Math.min(l1, l2);
  return (lighter + 0.05) / (darker + 0.05);
}

---

Common Failing Patterns

1. Light Text on Light Background

❌ FAILING EXAMPLE (from user screenshot):

┌─────────────────────────────────────────────┐
│  Background: #F5F2E8 (beige/cream)          │
│  Text: #C8FF00 (lime green)                 │
│                                             │
│     "Scan. Crawl. Match. Report."           │
│     ← UNREADABLE                            │
│                                             │
│  Calculated Ratio: ~1.5:1                   │
│  Required: 4.5:1 (normal) or 3:1 (large)    │
│  Verdict: FAIL by 3x                        │
└─────────────────────────────────────────────┘

✅ FIXED OPTIONS:
   • Darken text to #5A7300 → Ratio: 4.5:1
   • Darken background to #2A2A2A → Ratio: 12:1
   • Use dark green #1A4D00 → Ratio: 8:1

2. Gray Text Syndrome

❌ COMMON FAILURE:
   Background: #FFFFFF
   Text: #AAAAAA (light gray)
   Ratio: 2.3:1 ← FAIL

✅ FIXES:
   • Text: #767676 → Ratio: 4.5:1 (minimum AA)
   • Text: #595959 → Ratio: 7:1 (AAA)

3. Saturated Colors That Look Bright

❌ DECEPTIVE FAILURE:
   Background: #FFF8E7 (warm white)
   Text: #FF6B6B (coral/salmon)
   Ratio: 2.8:1 ← FAIL (looks "colorful" but fails)

✅ FIXES:
   • Text: #C62828 (darker red) → Ratio: 5.2:1
   • Text: #8B0000 (dark red) → Ratio: 8.1:1

4. Trendy Low-Contrast Aesthetic

❌ "MINIMALIST" FAILURE:
   Background: #FAFAFA
   Text: #E0E0E0
   Ratio: 1.3:1 ← SEVERELY FAILING

This is NOT minimalism. This is inaccessible.

✅ MINIMALIST + ACCESSIBLE:
   Background: #FAFAFA
   Text: #616161 → Ratio: 5.7:1

5. Placeholder Text Too Light

❌ COMMON FORM FAILURE:
   Input background: #FFFFFF
   Placeholder: #CCCCCC
   Ratio: 1.6:1 ← FAIL

✅ FIX:
   Placeholder: #757575 → Ratio: 4.6:1

6. Gradient Backgrounds

❌ VARIABLE CONTRAST:
   Gradient: #FFFFFF → #000080
   Text: #FFFFFF (fixed)

   Top of gradient: 1:1 (invisible!)
   Bottom of gradient: 8.6:1 (good)

✅ SOLUTIONS:
   • Add text shadow/outline
   • Use semi-transparent overlay behind text
   • Ensure ALL gradient stops pass contrast

---

Audit Methodology

Step 1: Visual Scan (Screenshot Analysis)

When given a screenshot, identify:

1. Text elements by size:

   • Headlines (large text → 3:1 required)
   • Body copy (normal text → 4.5:1 required)
   • UI labels (buttons, links → 4.5:1)
   • Captions/fine print (4.5:1 required)

2. Interactive elements:

   • Button borders/backgrounds
   • Form field borders
   • Focus states
   • Icons with meaning

3. Red flags to look for:

   • Light text on light backgrounds
   • Gray text on white
   • Colored text on colored backgrounds
   • Text over images without overlay

Step 2: Extract Colors

From CSS/code:

# Find all color declarations
grep -E "(color:|background:|#[0-9a-fA-F]{3,8}|rgb|hsl)" styles.css

From Tailwind:

# Find text/bg color classes
grep -E "(text-|bg-)" *.tsx *.jsx

Step 3: Calculate Ratios

For each text/background pair:

1. Convert colors to RGB
2. Calculate relative luminance
3. Compute contrast ratio
4. Compare to WCAG requirement

Step 4: Generate Report

# Contrast Audit Report

## Summary
- Total color pairs tested: X
- Passing (AA): Y
- Failing: Z
- Critical failures (<2:1): N

## Failures by Severity

### Critical (Ratio < 2:1)
| Location | Foreground | Background | Ratio | Required | Fix |
|----------|------------|------------|-------|----------|-----|
| Hero tagline | #C8FF00 | #F5F2E8 | 1.5:1 | 3:1 | #5A7300 |

### Moderate (Ratio 2:1 - 3:1)
...

### Minor (Ratio 3:1 - 4.5:1, normal text only)
...

## Recommended Fixes
[Specific color replacements with new ratios]

---

Color Blindness Considerations

Contrast requirements help but don't fully address color blindness. Additional checks:

Types to Consider

| Type | Affected | Consideration | |------|----------|---------------| | Deuteranopia | 6% of males | Red/green confusion | | Protanopia | 2% of males | Red appears dark | | Tritanopia | <1% | Blue/yellow confusion |

Best Practices

1. Never rely on color alone for meaning

   • Add icons, patterns, or text labels
   • Red/green for error/success needs icons too

2. Test problematic pairs:

   • Red + Green (stop/go)
   • Blue + Purple
   • Green + Brown
   • Light green + Yellow

3. Use sufficient lightness difference

   • Even with same hue, different lightness helps

---

Quick Reference: Safe Color Pairs

On White (#FFFFFF)

| Use Case | Color | Hex | Ratio | |----------|-------|-----|-------| | Body text | Dark gray | #333333 | 12.6:1 | | Secondary text | Medium gray | #767676 | 4.5:1 | | Links | Blue | #0066CC | 5.3:1 | | Success | Green | #2E7D32 | 5.1:1 | | Error | Red | #C62828 | 6.0:1 | | Warning | Orange-brown | #E65100 | 4.5:1 |

On Black (#000000)

| Use Case | Color | Hex | Ratio | |----------|-------|-----|-------| | Body text | Light gray | #E0E0E0 | 13.4:1 | | Secondary | Medium gray | #9E9E9E | 6.3:1 | | Accent | Light blue | #90CAF9 | 7.3:1 |

On Dark Gray (#1A1A1A)

| Use Case | Color | Hex | Ratio | |----------|-------|-----|-------| | Body text | Off-white | #F5F5F5 | 14.1:1 | | Secondary | Light gray | #BDBDBD | 8.3:1 |

---

Tools & Validation

Online Checkers

• WebAIM Contrast Checker
• Coolors Contrast Checker
• Adobe Color Accessibility

Browser DevTools

// Chrome DevTools: Elements → Styles → hover color swatch
// Shows contrast ratio automatically

// Firefox: Accessibility Inspector
// Shows color contrast issues

Automated Testing

// axe-core (popular a11y testing library)
const axe = require('axe-core');
axe.run(document, { rules: ['color-contrast'] });

// Lighthouse (built into Chrome)
// Performance → Accessibility → Color contrast

CLI Tools

# Lighthouse CLI
npx lighthouse https://example.com --only-categories=accessibility

# Pa11y
npx pa11y https://example.com

---

Integration with This Skill

When analyzing a screenshot or codebase:

1. I will identify all text/background color pairs
2. I will calculate contrast ratios for each
3. I will flag anything below WCAG AA thresholds
4. I will suggest specific hex values that pass
5. I will provide before/after comparisons

For the example screenshot (lime on beige):

AUDIT RESULT: CRITICAL FAILURE

Element: Hero tagline "Scan. Crawl. Match. Report."
Foreground: ~#C8FF00 (lime green)
Background: ~#F5F2E8 (beige)
Calculated Ratio: ~1.5:1
Required (large text): 3:1
Required (normal text): 4.5:1
Status: ❌ FAILS BY 2-3x

RECOMMENDED FIXES:
1. Darken text to #5A7300 (olive) → 4.8:1 ✓
2. Darken text to #3D5C00 (dark olive) → 7.1:1 ✓✓
3. Keep lime, darken BG to #3D3D3D → 8.2:1 ✓✓
4. Use #1B5E20 (dark green) → 8.4:1 ✓✓

---

Checklist for New Designs

Before shipping:

• [ ] All body text has ≥4.5:1 contrast
• [ ] All large text has ≥3:1 contrast
• [ ] All form borders have ≥3:1 contrast
• [ ] All icons conveying meaning have ≥3:1 contrast
• [ ] Placeholder text is readable (≥4.5:1)
• [ ] Focus states are clearly visible (≥3:1)
• [ ] Links are distinguishable without color alone
• [ ] Error/success states use icons, not just color
• [ ] Tested with color blindness simulators
• [ ] Automated accessibility scan passes

---

Philosophy: Beautiful design and accessibility are not mutually exclusive. High contrast can be striking, dramatic, and intentional. Low contrast isn't "minimalist"—it's exclusionary. Every unreadable word is a user lost.