Building Accessible Color Systems Without Waiting for contrast-color()

The CSS contrast-color() function promises to solve one of web development's most persistent accessibility challenges: automatically selecting readable text colors against any background. While browser support remains limited (Safari 26+ only as of 2024), we don't need to wait. Modern CSS features can approximate this functionality surprisingly well.

The Core Challenge: Making Colors Accessible by Default

Every developer has faced this scenario: you have a dynamic background color—maybe from user themes, hover states, or a design system palette—and you need to ensure text remains readable. The manual approach of pairing specific colors breaks down quickly:

1/* Brittle manual approach */
2.button-primary { background: #007bff; color: white; }
3.button-success { background: #28a745; color: white; }
4.button-warning { background: #ffc107; color: black; /* Wait, why black here? */ }

The contrast-color() function would eliminate this guesswork:

1/* Future CSS - limited browser support */
2.button {
3  background: var(--button-color);
4  color: contrast-color(var(--button-color));
5}

But we can build this behavior today using luminance calculations and CSS custom properties.

The Mathematics of Readable Text

The secret lies in relative luminance—a measure of how bright a color appears to human vision. The WCAG formula weights RGB channels differently because our eyes are more sensitive to green than red, and much more sensitive to red than blue:

This formula gives us a brightness value between 0 (black) and 255 (white). Colors below ~128 need light text; colors above need dark text.

Here's how to implement this in pure CSS using the @property feature:

1@property --luminance {
2  syntax: "*";
3  inherits: false;
4  initial-value: calc(((r * 0.299) + (g * 0.587) + (b * 0.114) - 128) * -1000);
5}
6
7.dynamic-contrast {
8  --bg-color: #7c3aed; /* Any color */

The * -1000 multiplication amplifies the result: negative values (dark backgrounds) become very dark (approaching black), while positive values (light backgrounds) become very light (approaching white).

Beyond Black and White: Modern Color Spaces

While RGB luminance works, modern CSS offers more sophisticated approaches using OKLCH and LCH color spaces. These provide perceptually uniform brightness adjustments:

1.oklch-contrast {
2  --base-color: oklch(0.7 0.15 280); /* Purple */
3  background: var(--base-color);
4  
5  /* Flip the lightness value */
6  color: oklch(
7    from var(--base-color) 
8    calc(100% - l) 
9    c 
10    h
11  );
12}

This approach inverts the lightness channel while preserving chroma and hue, often producing more visually appealing results than pure black/white.

For subtler contrast that maintains color relationships:

1.subtle-contrast {
2  --accent: oklch(0.6 0.2 200); /* Teal */
3  background: var(--accent);
4  
5  /* Shift lightness by 40% for readable contrast */
6  color: oklch(
7    from var(--accent) 
8    calc(l + 0.4) 
9    calc(c * 0.8) 
10    h
11  );
12}

Real-World Implementation Strategy

For production systems, combine multiple techniques with progressive enhancement:

1:root {
2  /* Fallback colors for unsupported browsers */
3  --text-on-primary: white;
4  --text-on-secondary: black;
5}
6
7/* Enhanced browsers get automatic contrast */
8@supports (color: oklch(from red l c h)) {

Browser Support and Fallbacks

The @property approach works in Chromium browsers (Chrome, Edge, Opera) but requires fallbacks for Firefox and older Safari versions. For broader support, consider a hybrid approach:

1.universal-contrast {
2  /* Fallback for all browsers */
3  color: var(--fallback-text-color, black);
4  
5  /* Enhanced for modern browsers */
6  color: light-dark(
7    oklch(from var(--bg-color) calc(l - 0.6) c h),
8    oklch(from var(--bg-color) calc(l + 0.6) c h)
9  );
10}

The light-dark() function automatically selects appropriate colors based on the user's preferred color scheme.

Why This Matters Now

Building accessible color systems shouldn't wait for universal browser support. These techniques provide:

• Immediate accessibility wins: WCAG-compliant contrast ratios without manual color management
• Future-proof code: Gradual enhancement as contrast-color() gains support
• Design system scalability: One formula handles infinite color combinations
• User preference respect: Integration with prefers-contrast and prefers-color-scheme

Start with luminance-based calculations for critical text, then enhance with modern color spaces where supported. Your users—and your future self maintaining complex color systems—will thank you.

The web's accessibility future is arriving in pieces. Rather than waiting for the complete picture, we can build inclusive experiences today with the tools already in our browsers.