/**
 * Hand-mirror of game/src/engine/hud/colorMath.ts — the WCAG arithmetic behind
 * the derived HUD inks. The theme report computes its contrast pairings with
 * EXACTLY the maths the engine will apply, so a SUBSTITUTED line in the report
 * is a promise about what will render, not an estimate.
 *
 * Mirrored by hand because agent tools cannot import engine source (separate
 * tsconfig include sets). Drift-checked BEHAVIOURALLY by scripts/
 * check-hud-catalog.ts: the gate imports both copies under tsx and compares
 * their outputs over every preset palette plus adversarial pairs, so a changed
 * threshold or mix factor on either side goes red in CI.
 */
export declare function relLuminance(hex: string): number;
export declare function contrastRatio(a: string, b: string): number;
export declare function mixHex(from: string, to: string, amount: number): string;
export declare function readableTextColor(hex: string): string;
export declare const ON_SURFACE_MIN_CONTRAST = 3;
export declare function inkOnSurface(surface: string, preferred: string): string;
export declare const ACCENT_INK_MIN_CONTRAST = 4.5;
export declare function accentInkOn(ground: string, accent: string): string | null;
export declare function mutedInkOnSurface(surface: string, preferred: string): string;