Color makes no difference, silkies are very difficult to sex before 4-5 mos. of age (and that is by experienced breeders). Sometimes you have to wait till it crows or lays an egg. It is extremely easy for unscrupulous sellers to dump very young birds on someone and claim they are the preferred sex. They figure by the time you discover what sex the bird is, you are too attached to it to complain.
If you definitely cannot have roosters, do not buy a young bird.
If you definitely cannot have roosters, do not buy a young bird.