I don't think there is a 'pink phase' pattern at all. Neither my DD or 4 nieces growing up in the 80s/90s showed any sign of excessive devotion to pink, nor, BTW, did I or my sister. If it is a 'natural' pattern girls in the Victorian era would have been extremely pee'd off because pink was a 'boy's colour' back then. It's culturally induced. Which is the point I was trying to make earlier today.
I don't think that I (or my sister) had a 'pink phase', although I very much doubt that we'd have been indulged if we had! It was definitely the case for my lot and their friends, though, as well as for my sister's children and their friends. They are in a different part of the country, so it's not a local thing, and it holds true today - at the age of four or five the little ones in the family want everything in pink, and by seven or eight they'd rather have any other colour.
I didn't say it was 'natural' - in fact I said the opposite - and just wondered what it could be, given the geographical, time and other differences between the children. Of course it has to be culturally induced, but I don't think that four year olds are particularly susceptible to advertising, are they? I don't think mine saw a lot of TV at that age, but I may be misremembering. And anyway, if it were an advertising-induced thing, why would they stop it at seven or eight when there would still be money to be made? The Argos catalogue, and the aisles at ToysRUs were very gender specific if I remember rightly, so maybe they picked it up from there. I'm just thinking aloud though (sorry), so ignore me?