/**
 * Checks whether the given string is a recognized color format.
 * Supports hex, rgb/rgba, hsl/hsla, and CSS named colors.
 */
export declare const isValidColor: (color: string) => boolean;
/**
 * Converts any supported color string to a lowercase hex representation.
 * @throws {PaletteError} if the color cannot be parsed.
 */
export declare const toHex: (color: string) => string;
/**
 * Shifts a hex color's lightness in CIE-LAB space.
 * Positive `amount` darkens, negative `amount` lightens.
 * Compatible with chroma.js darken/brighten (Kn = 18).
 */
export declare const shiftLightness: (hexColor: string, amount: number) => string;