Thank you so much. I will try to get some pictures tonight. She has only ever been in the same pen with a white male so one must be recessive. I thought I had heard you could never know what color you will get when you mix a white with another color, I just didn't know that about 2 whites. I'll have to try and get closer, they could be blue. Mama just didn't let me get to close last night.Hmm that is a tricky one. Is there any chance another rooster had access to her in the last month? I've heard of hens being fertile a month after mating sometimes.
If your hen definitely did not have any access to any other roosters than all my theories involve one of your whites not truly being white. A very lightly marked paint or a very washed out splash might give you some blackish looking chicks if bred to a recessive white (if it was a really washed out splash those chicks would actually be blue but blue can look very dark almost black sometimes).
I'm still learning about genetics but I have done a lot of research and have experienced some things first hand now I'm getting into breeding so hopefully this information is at least mostly accurate.
White silkies can either be recessive white or dominant white. Reccessive white is much more common and has been around a lot longer in silkies. I don't think dominant white really came into play much until colors like paint were developed rather recently (paint relies on dominant white to work).
A recessive white silkie needs two copies of recessive white to be white. If bred to another recessive white the babies should all be white. Recessive white works by basically turning off the pigment resulting in white. There is still genetically another color underneath that is being hidden/turned off by the two copies of the recessive white gene. Unless you test breed you can't really know what color might be underneath. When you breed a recessive white to a non recessive white that color that was being turned off comes into play whatever it may be which is why it is very difficult to predict the outcome of a breeding of most white silkies with a non white.
Dominant white on the other hand only needs one copy to express but it is considered leaky. It inhibits black pigment ( it works on genes that modify black pigment like blue and splash as well) but does not inhibit red. With only one copy of dominant white some of the black pigment comes through in spots (sometimes only a few very small spots other times much more obvious spots). With two copies of dominant white usually no black comes through and the bird appears all white assuming there is no red involved in the genetics.
Pictures of the parents and chicks might be helpful in trying to figure out what is going on genetically if you have or can get some?

But I am so good with that. Blue silkies are my favorite. I'm thinking maybe my white girl might have some splash to her. I moved her and her babies the other night and I think she has little splashes of color I had never seen before. Surprise!!!

