Are you saying you saw a black chick one day, and the same chick is now mostly white? Chick color can certainly look different when they are wet vs. dry, but that is quite a significant change.
Are you talking about the EE cockerel in this post?
That cockerel does not have the gene called Dominant White.
Dominant White turns black to white. It may miss a few bits here and there (leakage, or a "paint" chicken), but it is clearly not acting on that cockerel.
That cockerel probably has Silver (a dominant gene that turns gold to white, although it allows some red shades to show in places like rooster shoulders and hen breasts.) But we call that gene Silver, even though it is dominant and causes some parts of the chicken to be white in color.
If the mother was a White Leghorn, the chick's color probably came from her.
The E gene ("Extended Black") makes a chicken black all over, is dominant, and overrides the effect of most other genes. White Leghorns tend to be E/E (pure for the Extended Black gene.)
Dominant White turns all the black to white. White Leghorns tend to be pure for Dominant White, too.
So every chick from a White Leghorn crossed with anything else will have E and Dominant White, making it white with some bits of black leakage. It's one of the most predictable results when crossing different chicken breeds.
I'm not as sure about what's going on with the other ones, but it may become more obvious as they grow their feathers over the next few months.
patches:
