Contrast and color

Contrast and Color

Instructions

Contrast failures are the single most common accessibility bug in mobile apps. Treat color decisions as engineering decisions with measurable acceptance criteria.

1. Contrast Ratios (WCAG 2.2 AA)

Content	Minimum ratio
Body text (< 18pt regular, < 14pt bold)	4.5:1
Large text (>= 18pt regular or >= 14pt bold)	3:1
Icon / graphical UI component	3:1 (1.4.11)
Focus indicator outline	3:1 vs adjacent colors
Disabled states	Exempt from 1.4.3 but still should aim for 3:1 where possible

For AAA (optional), raise body text to 7:1 and large text to 4.5:1.

2. Measuring Contrast at the Token Level

Do the math once, at the design-token layer; do not eyeball it per screen.

// utility — WCAG relative luminance
fun luminance(c: Color): Double {
    fun ch(x: Float): Double {
        val v = x.toDouble()
        return if (v <= 0.03928) v / 12.92 else Math.pow((v + 0.055) / 1.055, 2.4)
    }
    return 0.2126 * ch(c.red) + 0.7152 * ch(c.green) + 0.0722 * ch(c.blue)
}

fun contrast(a: Color, b: Color): Double {
    val la = luminance(a); val lb = luminance(b)
    val (hi, lo) = if (la > lb) la to lb else lb to la
    return (hi + 0.05) / (lo + 0.05)
}

require(contrast(Tokens.onSurface, Tokens.surface) >= 4.5)

Add a unit test that fails if a token pair drops below threshold.

3. Do Not Rely on Color Alone (WCAG 1.4.1)

Pair color with a second cue:

• Form errors → red border and error icon and text.
• Required fields → asterisk with the text "required" (visually hidden or in label).
• Status chips → color and icon (check / warn / info).
• Graphs → color and pattern (dash, dots) and direct labels.

SwiftUI status chip:

Label {
    Text("Payment failed")
} icon: {
    Image(systemName: "exclamationmark.octagon.fill")
}
.foregroundStyle(.red)
.accessibilityLabel("Error. Payment failed.")

4. Color-Blind-Safe Palettes

Roughly 1 in 12 men and 1 in 200 women have some color vision deficiency (CVD). The three concerns:

• Red/green (protanopia, deuteranopia) — most common. Never rely on red-vs-green alone (profit vs loss, pass vs fail).
• Blue/yellow (tritanopia) — rarer.
• Full achromatopsia — treat the UI as if it were grayscale.

Safe strategies:

• Differentiate by hue + lightness + icon/pattern, not hue alone.
• Prefer palettes with monotonic luminance (e.g., ColorBrewer qualitative / sequential).
• Validate with simulators (Sim Daltonism, Chrome DevTools Rendering panel).

5. Disabled and Placeholder Text

Low-contrast disabled text is tempting visually but confuses everyone.

• Keep disabled text at >= 3:1 where possible.
• Use a secondary cue (icon, "(disabled)" suffix in a11y label) so users relying on AT know.
• Placeholder text is not a substitute for a label. And it must meet contrast too.

6. Focus and Selection Indicators (1.4.11 / 2.4.11)

Focus outlines, selection highlights, and progress bars must contrast 3:1 against the surrounding color — in both themes.

// SwiftUI
.overlay(
    RoundedRectangle(cornerRadius: 8)
        .stroke(isFocused ? Color.accentColor : .clear, lineWidth: 2)
)

// Compose
Modifier.border(
    width = 2.dp,
    color = if (isFocused) MaterialTheme.colorScheme.primary else Color.Transparent,
    shape = RoundedCornerShape(8.dp)
)

7. Dark Mode Pitfalls

• Pure #000 backgrounds with pure #FFF text create "halation" for astigmatism users. Prefer #121212 with #E6E6E6.
• Elevation shifts must still provide 3:1 boundary contrast.
• Verify brand accent colors in dark; many fail 3:1 against #121212.

8. High Contrast System Settings

Honor user overrides:

• iOS: UIAccessibility.isDarkerSystemColorsEnabled (Increase Contrast). Provide a higher-contrast variant of your token set.
• Android: Settings.Secure.high_text_contrast_enabled — rendered automatically by the system for text, but still test custom drawables.

@Environment(\.accessibilityShowButtonShapes) private var showButtonShapes
// render bordered buttons when true

9. Tools

• Stark, Figma Contrast, Able plugins at design time.
• Accessibility Inspector (macOS) → Audit tab → contrast warnings.
• Accessibility Scanner (Android) flags low-contrast views.
• Chrome DevTools Rendering — simulate CVD when viewing mobile web views.
• Token-level unit tests (see §2).

10. Common Pitfalls

• Hero marketing screens with light text on photo backgrounds — add a scrim or read-gradient.
• Gradients crossing contrast thresholds mid-element — sample at the text bounding box, not the average.
• Gray-on-gray secondary metadata that fails at 4.5:1.
• Focus rings removed for "aesthetics".
• Using Color.red semantic meaning without a non-color backup.

Checklist

• Token pairs verified at 4.5:1 / 3:1 via automated test.
• No info conveyed by color alone.
• Disabled states still readable or clearly marked in AT.
• Focus indicators meet 3:1 in light and dark themes.
• Dark-mode palette avoids pure black + pure white.
• CVD simulation passes for critical flows (checkout, error states, charts).
• High-contrast system toggle tested on iOS and Android.