It's likely as what others have said for when the colour 'pink' became acceptable for males.
I just wonder if colours attributed to both sexes were always the same across all cultures or histories. I don't think so. I read this article from The Times online dated August '07. "We all know that women like pink"(bah) because it's a reminder of our hunter-gatherer days and boys 'prefer' blue. Women would pick red fruit and then pink is a form of it. Pink connotes emotional states. Boys would choose blue.The study which the article was based on involved only British Caucasians and Chinese Asians yet they make it seem conclusive that it translates for all of both sexes-- I don't trust the article once ounce of sweat but people can be easily influenced to believe such things... "At last, science discovers..."!!! Bah. People perpetuate preferences from their conditioned brainwashing as children, for the most part. Stop pink from being a "girly" colour, thrust it onto males and 100 years from now "all" boys might just prefer it over blue (/) and females might all like green ( <---Bah) I know, for myself, I intensly hated the colour pink (or barbies/dolls). I probably influenced my little sis to hate it too. My best/f hated it on her own. I should add, also, that I believe it's when I became aware what pink was associated as being for females. I have physical evidence that I wore pink up to age 4/5 (and with flowers--). But that was my mother's doing. So, once I became aware, I rejcted it (Phew!). I'm somewhat okay with it now, though. Small doses. I cringe if I see females dressed in all pink. Such as on Maternity floors..all in pink, bags, shoes, makeup, all, even their new daughters.. <---even that stupid hanky is pink! Oi vey!While blue was liked universally, this preference stood out among men as it was not balanced by a parallel liking for pink, the study found. This, too, could have deep-seated natural roots: water that appears blue is more likely to be clean, and the colour is also an indicator of fine weather.
But if they're right about pink connoting emotional states, I'd think it only likely because we've associated it as being so for so long. So, males liking pink now might mean that they've become more "emotionally" accepting. It's becoming acceptable to have emotionally open and aware males. I think that might've been when it became acceptable for males or a big part of it.
Hey, maybe females changed from liking red to pink due to menses? And males disliked red for that reason too!