/**
 * The colour a `w:shd` actually paints: its `w:fill` background with the
 * pattern colour blended in at the pattern's density. `clear` (and an absent
 * `w:val`) is the fill alone; `nil` paints nothing.
 *
 * @param val   `w:val` — the pattern.
 * @param color `w:color` — the pattern's own colour (`auto` ⇒ black).
 * @param fill  `w:fill` — the background (`auto` ⇒ white).
 * @returns The 6-hex colour to paint, or `undefined` when nothing is painted.
 */
export declare function shadingFillHex(val: string | undefined, color: string | undefined, fill: string | undefined): string | undefined;