What would cause a barred rock to have one white feather on each wing? She's still a young pullet (9 or 10 weeks, I'd have to check my records) but so far that feather looks very similar to a young slw of the same age's feathers.
Could you add pictures? If it’s a hatchery bird, I wouldn’t worry about it. It also might just be juvenile feathers coming in, the adult feathers should grow in without any white feathers like you described.
Sometimes hatchery quality BRs will have a couple solid white feathers or solid black feathers. Hatchery quality birds aren't perfect and sometimes the coloring isn't very strong (meaning the genes aren't very strong) (I think that's how it works???) Happens with black australorps, too- they'll have a couple white feathers.
I didn't think I could get a picture in the dark but you replied so fast I had to try. This was the best I could do because she didn't like how cold my hands are and that white rock in the picture was throwing a fit about the flash. I had thought she would lose this feather eventually like you said but it's been getting whiter and I just noticed taking the picture that the other feather near it is a lot lighter than it used to be.
To be honest I hope she keeps it. She's so friendly that she's the only hen that I let my son name, he named her penny. Would be a shame if I couldn't tell her from the rest.