Amusingly enough, “blue hairs” has long been slang for elderly women - a lot of old women used to put a bit of bluing in their yellowish grey hair to make it look whiter/more silvery, and some of them overdid it a bit at times.

What’s bluing? A non-permanent blue dye that used to be used when rinsing white shirts to make them look less yellowed. It’s still sold, but I don’t know anyone under 60 who still buys it.

Amused by this shift in meaning, mostly because I’m now the female equivalent of a “grey beard” in tech, old enough to have experienced the Dotcom bust - there is a fair bit of silver in my hair, and I can’t be bothered to cover it. “Grey bun”?