export interface HCT {
    hue: number;
    chroma: number;
    tone: number;
}
/**
 * Convert a hex color to HCT.
 * Hue: 0-360, Chroma: 0-~120, Tone: 0-100.
 */
export declare function hexToHct(hex: string): HCT;
/**
 * Convert HCT to hex, with gamut mapping.
 * Uses chroma reduction to find the closest in-gamut sRGB color.
 */
export declare function hctToHex(hct: HCT): string;
/**
 * Generate a tonal palette: hex colors at standard tones
 * for a given hue and chroma.
 */
export declare function tonalPalette(hue: number, chroma: number): Record<number, string>;
/**
 * Append alpha (0-1) to a hex color as a 2-digit hex suffix.
 */
export declare function hexWithAlpha(hex: string, alpha: number): string;
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