Did I 'trans' my son who said he didn't like pink?
No. Because what he was communicating was that he was associating with markers of being a boy, so there is zero indication at all that my son is gender non-conforming, gender questioning, gender dysphoric or trans.
If it had been the opposite, and he indicated a mild preference for pink, say, would I then have 'transed' him? Also no, because that is not the sort of strident and persistent attempt to associate with things society has told him are markers for girls.
On the other hand, if he would only play with 'girls' toys, only wear 'girls' clothes or 'girls' colours, and had an extreme adverse reaction to anything associated with boys, that may well indicate that he is trying to communicate in the way society has taught him that he is a girl.
But even then it would only be one indicator. If unaccompanied by other indicators, it would still not be a basis to assume that he is trans. But if accompanied by other indicators, and his preference were to be treated as a girl, referred to with girls pronouns etc, then yes, at that point I would allow my son to present in a way that made his life easier and respected his own knowledge about himself. And if he changed his mind later, he would still have my full support. Because even at five, my son knows plenty about him and I have built a relationship with him of respecting that and only overriding when its essential for his wellbeing or safety.