This! ^ And I think the OP's husband is entitled to not like it if he has known her/been with her for 30+ years and it's always been mousy or brown (not sure what OP's hair colour is as she has not said.)
Women on here are happy to say they hate their partner's beard, so the OP's husband can say he doesn't like her grey hair. Your life partner has a right to an opinion on you changing how you look. Even so, if the OP wants to let it go grey then crack on. Odd for people to comment about it being unprofessional though. Maybe they think it looks a mess? I don't know. (With mixed colours/neither one colour or another?) I would have to see it to give a proper opinion.
I am mid-late 50s, and my natural hair colour is dark blonde. Only just started to go grey at the temples in my mid 50s. Going grey at a much older age is common in my family. I just dye my hair blonde every 2 months and the roots get done with it. I won't be going grey any time soon.
I know a number of women in their 70s and 80s, and a few in their 90s, who still keep their hair blonde, or mousy. Refuse to go grey. Good for them! I am sick of women being slated (especially on here) for having the audacity to not want to show their grey hair, and the women who show the grey as young as 40 are considered better people/empowered/stronger.
It's misogyny. It's no better than slating women for having lip filler - or false eyelashes and false nails. Let women do what they want, and stop shaming them for wanting to dye their hair and keep the grey at bay, (whilst celebrating the women going grey - like they're some kind of hero!) Trying to make women feel bad for hiding the grey, with the guilt-tripping trope 'be grateful you are ageing, some people don't get that privilege!' is manipulative and cruel. Just stop it already!