I got two red stars at the feed store in august and now that they are fully feathered, they have mostly black tail feathers and a few black/red one throughout their body and one has some on her neck. Do red stars normally have some black feathers?
Random black feathers occur in a lot of chickens, even in pure white ones. The odd or misplaced feathers are usually a sign of an impurity in the line, like a hybrid in the ancestry. Seeing how you're hens are a hybrid breed for a friendly and good layer chicken it shouldn't raise any alarms.
I personally like the hybrids, I just got one, but she's a black sexlink not a red:
I think it just depends on the mix used to make the sex link. I've seen birds on here folks say were bought as sex links that have black points, where most of the sex links have white. Just a different recipe, I believe.