It’s considered a fault if you’re trying to breed for recognized Silkie colors. it is definitely a fault in showing. If you’re just breeding for fun and have a mixed color flock, then it doesn’t really matter.
As an example, I bred my paint Silkie rooster to a mixed partridge hen.
All the chicks were either black or paint but as they grew some of them showed leakage from the partridge mom.
Here are 2 of the pullets at 4 months of age.
One is completely black and the other one has the red leakage in the hackle feathers.
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Leakage can come from many colors, so it can be difficult to say exactly where it came from in your roosters.
With your black rooster with silver leakage and your black hens you will likely get black chicks with silver leakage especially in the males.
It will also depend if your black hens are recessive for any other colors. For example in my solid black pullet above, you would not know she was carrying partridge unless she was bred to another bird that carries partridge or other similar colors.