She was a woman, Nonu not a trophy bimbo to be exhibited on "occasions" like a Stepford wife.
Why should she dye her hair? There is nothing to be ashamed of in grey hair. and the earliest first ladies certainly did not do so. They would have been either "shameless hussies" or ridiculed for trying to be "mutton dressed as lamb".
It is only fairly recently that the cult of everlasting youth has persuaded women in public life that they must never look their age, or anywhere near it, but must give the impression that their eminent (and grey or bald) husbands are married to eternal teenagers.