We rehomed 3 ex-battery hens this year, then got a couple of brahmas (cock & hen) in the summer. So far no health problems, had a bit of a red mite issue in the summer but we managed to get rid of that.

I've noticed this past week or so that one of our ex-batt hens (Blanche) has had alot of the feathers on her neck turn white. Not all but flecked, also her tail feathers. What could be causing this? Vitamin deficency? She seems her usual bossy self, not off her food or anything but I've always kept more of an eye on her as she wazs the one most affected by the red mites.

Any thoughts of why this is happening?

Could just be they are old feathers ready to moult - they can sometimes look tatty and bleach a bit, or that could just be her markings coming through - my batteries are ISA warrens and a few have white tails and white edges to some feathers, especially their neck feathers - just their particular patterns - they are not all a uniform orange/brown - I think they are very pretty birds!
Forgot to put it could also be age - the older they get sometimes white feathers do appear after each molt where before there were none!

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They looked really tatty when we first bought them home then even worse as they began their moult.

I think it may be, as you suggested, that her true markings are coming through or age. It looks very pretty as the white feathers on her neck look almost like a pattern. I just wanted to check in case it was a deficiency of some sort