That silver gene is the holy grail for breeding whites from what little I've read. I will need to get some good books on genetics if I want to do my breeding correctly. Silkies were one of the first breeds to be accepted into the ASOP nearly 150 years ago. There have been a lot of genetic studies done on them over the decades and most of that knowledge is in books not on the Internet. I like books. Need to start adding to my library.
@Aoxa: About your question on Whites fading or getting brassy in sun: My property is mostly shade. The breeding pens in my barn open into shaded runs and paddocks. Fading and brassiness in whites has not been a problem for me. Also about breeding whites. I don't put a lot of corn in their feed when conditioning for show. And it goes back to genetics again. You can breed brassiness out of a white flock. It takes careful record keeping and progeny testing.
Birds in my barn that are destined for breeding I consider valuable. I don't take risks with them for head injury pecks from larger roosters or even dominate hens. Quality birds are hard to come by where I live. Not easy to replace.