White in silkies is almost always recessive. There is a separate dominant white gene, but it is usually very leaky--allowing other colours to express in certain areas. Recesive white is very much not leaky. If a bird has two copies of it, you have no idea of what other genetic colours or...
Silly me, you said "cock" and I read "rock." Anyways, may last statement is correct--unpredictable no idea what the white cock is hiding, genetically speaking
Non-bearded silkies tend to have large wattles--even the girls.
Aren't white rocks dominant white? if so, then offspring would be white. If recessive white then it's hard to say what the rocks could be hiding.