White in silkies is almost always recessive. In any case, you do not really know what colours it has genetically present beyond white, which is a switch the prevents colour in the feathers. Mixing white with any other colour is unpredictable. Two different white birds can have completely different sets of genes--the only colour/pattern genes they definitelly have in common is white.
Crest, black skin, feathered feet, muff/beard and polydactyly are dominant traits and will show if one parent has them.