A white cat breeds as both a white (which you see) and a masked color (which you don't see) and can produce based on both white and the unseen color/pattern. The masked color/pattern must be determined, based on the white's pedigree and the offspring produced in a controlled breeding, in order to effectively predict the color/pattern of the expected offspring. Interestingly, white kittens may have a small spot of color on top of their heads when born. This color should be noted as it is the color that the white is masking and the color that the cat will breed as when an adult. The spot of color may be visible for several months, but often disappears as the kitten matures.