/**
 * Whether given foreground and background colours meets WCAG 2.0 AA contrast ratio.
 * @param foreground the foreground colour
 * @param background the background colour
 * @returns true if the contrast ratio is greater than 4.5; false otherwise (or if one of the colours are invalid)
 */
export declare const isMeetsWcagAaRatio: (foreground: string, background: string) => boolean | null;
/**
 * Get the contrast ratio between two colours.
 * @param foreground the foreground colour
 * @param background the background colour
 * @returns the contrast ratio, or null if the colours are invalid
 */
export declare const getContrast: (foreground: string, background: string) => number | null;
export declare const getContrastColor: (fg: string, bg: string, fallback: string) => string;