/**
 * WCAG 2.x contrast ratio utilities (pure, deterministic).
 */
export interface Color {
    r: number;
    g: number;
    b: number;
    a: number;
}
/**
 * Parse a color string into RGBA components.
 * Handles: #rgb, #rgba, #rrggbb, #rrggbbaa, rgb(), rgba(), hsl(), hsla()
 * (both comma-separated and CSS Color Level 4 space-separated), and named colors.
 * Returns null if unparseable.
 */
export declare function parseColor(s: string): Color | null;
/**
 * Calculate relative luminance per WCAG 2.x sRGB.
 * Input: { r: 0-255, g: 0-255, b: 0-255 }
 * Output: 0-1 (0=black, 1=white)
 */
export declare function relativeLuminance(c: {
    r: number;
    g: number;
    b: number;
}): number;
/**
 * Calculate WCAG contrast ratio between two colors.
 * Returns null if either color is unparseable or has alpha < 1.
 * Otherwise returns contrast ratio (1-21).
 */
export declare function contrastRatio(fg: string, bg: string): number | null;