It is interesting though. In society things like dyeing your hair, fake tan, plucking your eyebrows, wearing make up, are all seen as very feminine and often even desirable in a woman.
Yet when a man does these things it's seen as unattractive, vain, effeminate, cringe worthy, laughable.
Society places very different values on that vanity. And they are gender based.
I think where this thread is unusual, is most women would tell their husbands not to be daft, he looks gorgeous, that men are perceived as attractive with grey hair, that he suits it, but the op seems very keen to get stuck in about his hair.
Does she wish to make her husband unattractive to other women? She's even happy for him to have a short lived mistake, so basically him walking about with a right bad dye job for a month, looking like a twat, and everyone to know.
As we have seen by this thread, it's not the normal reaction from most women.