DS2 (3) likes pink as well.
Since starting school, DS1 (5) has told DS2 on several occasions, when they've been given the choice of picking something that comes in several colours (water bottle most recently), that pink is for girls so DS2 should pick something else.
I've told them that boys can have the pink one if they like, but DS1's clearly picked up on peer pressure at school that he shouldn't be playing with or using pink things as they're for girls and he's a boy.
The subtle reinforcement that certain toys / activities are mainly for either girls or boys (shown by the handy e.g pink = for girls colour code), rather than all toys / activities being okay for all children, doesn't do anyone any favours.