If you mix a pure white silkie with any other colour, it's going to bring up differences in the chicks. I'm not sure what you mean by this? For example, I know a breeder who only works with whites, and has only worked with whites for 15 years. Those whites would not be hiding any colours, but if you took one of those and bred it to a blue for example, you're going to get chicks that are not pure in colour - that's a given. But I can't imagine there being a hidden colour under 15 years of breeding whites..?even if the breeder IS highly regarded, there is no way to know. With whites you cannot elective choose which of the hidden genes to breed for or against, so it is a hodge podge, regardless of the breeder.
Maybe I am reading your statement wrong. Probably. It's early.