This is not always so, not in all stocks !
Ask Tünde about Black- and Blue-Silver cocks she had of mine, was one with a very dark crest. (he was not so good in shape) but such ones you should breed in only to select on for the coloration of the crest.
Another thing is the "groundcolor", these of Black, Blue, Splash, Grigioperla should be "E/E", these of white should be "eb/eb" and that makes a difference.
Read about here :
sites.google.com/site/zijdehoenders/t%26dcreating/basics-about-chicken-color-genetics-heritage/breeding-specialitity-knowledge-about-e-e-groundcolor...
and here :
sites.google.com/site/zijdehoenders/t%26dcreating/basics-about-chicken-color-genetics-heritage/breeding-specialitity-knowledge-about-eb-eb-groundcolor...