i fthat is what he wants, and you've talked to him baout potential repercussions form his peer group, and he still wants it - go ahead!
my dss bought a (very nice) pink shirt while he was staying with us a few years ago. he went out shopping with a mate, came back with a few bags, and when we asked what he'd bought said "oh, well, you'll probably hate it - it's not what you'll be expecting".
both dh & I loved it - dh wears the odd bit of pink here and there - and dss was peasantly surprised by our attitude.
sadly, his sister then came in (my dsd) and laughed. lots
dss must have been about 14 at the time, so dsd was 15 or so. anyway, upshot of it all - dss went home, and I can only assume his mother also did not approve as the shirt was never seen again.
very sad, as was the first time he'd taken an interest in shopping too.
as other posters have said - it's just another colour, and if pink is what he wants then go for it.