If they are solid white, they could remain that way or they could have "pointed" markings (siamese markings) as pointed markings are directly related to temperature, while the kitten is warm inside momma's tummy, they are white but after they are born they slowly develop tan/brown coloring on their face, ears and tail and possibly on their paws (depending on whether they carry the "white socked" gene) as well, the coat over the rest of the body typically turns tan.