Merriam-Webster Collegiate Dictionary - mottle

 I. noun  Etymology: probably back-formation from motley  Date: 1676  1. a colored spot  2.  a. a surface having colored spots or blotches  b. the arrangement of such spots or blotches on a surface  3. mosaic 5  • ~d adjective  II. transitive verb  (~d; mottling)  Date: 1676 to mark with spots or blotches of different color or shades of color as if stained  • ~r noun