Yes, whitest is a Scrabble word!

Adjective

1. Being of the achromatic color of maximum lightness; having little or no hue owing to reflection of almost all incident light

2. Of or belonging to a racial group having light skin coloration

3. Free from moral blemish or impurity; unsullied

4. Marked by the presence of snow

5. Restricted to whites only

6. Glowing white with heat

7. Benevolent; without malicious intent

8. (of a surface) not written or printed on

9. (of coffee) having cream or milk added

10. (of hair) having lost its color

11. Anemic looking from illness or emotion

12. Of summer nights in northern latitudes where the sun barely sets