Summer parenting is about making joint decisions. Finding compromises and working as a team.
This baby will belong equally to you both. So the pram has to be something you both agree on. Same with the name and a hundred other decisions.
Regardless of whether you think his reasons are silly or not he doesn’t want a pink pram. He’s allowed a veto just as you are. You don’t want a black pram. Fair enough find a colour you both agree on.
A nice strong red can be a good compromise. Or navy if you plan to have pink liners etc.
It sounds like the root of your concern is that you are upset that he is disappointed that it’s a girl.
That’s completely understandable but pushing him into a pink pram he doesn’t like is more likely to make him withdraw and presumably you want him to be more engaged not less.
The colour of the pram is the least important thing about it tbh.
Find a compromise.
Regarding clothes, the baby can wear frilly dresses and joggers. It’s not either or. (But don’t buy those cute dresses with ruched bodices - nightmare to iron).
To make you feel better, I know two men who were extremely vocal about wanting a boy who got girls. Both men are absolutely besotted with their daughters, even though they both also now have boys.
Wait until he holds her, he’ll fall head over heels in love in about half a second. Don’t waste energy arguing over a pram colour.