Black Cat Rapidly Turning Gray?

I have a female black cat (DSH) that is suddenly getting a LOT of gray hairs. Her ears, under her collar (?) under her "arms," and now starting to just sprinkle throughout her body. She is a former feral that the vet guesses to only be a couple of years old. She had 8 kittens in April that we kept and she nursed until 10 - 12 weeks. THEN she had an intestinal obstruction that required surgery.

Soooo...had anyone encountered this - maybe some breeds lighten up in the summer (her collar area) & it's been HOT here , or stress? Her fur also seems shorter - maybe shedding the outer coat and this is the under coat?

Had lots of black cats, and never had this happen before...

Thanks, Kim.

It might be a hormonal thing. I know that if black cats don't get enough tyrosine, they "rust" or turn brownish.