thanks TheTimesMNer that has set me off on a search. It started in about the 1920s with pink for boys (since pink was a strong watered down red colour and associated with masculinity). Blue is a colour associated with the Virgin Mary, don't know why that is, interesting if anyone knows why, so blue was the colour for girls. After the war it changed round, basically for commercial reasons, as pink was promoted to women to match lipstick and blushers.
Before that all children were usually dressed in white or possibly blue.
Some alternative explanations are
"
In almost every culture, one stereotype emerges: pink is associated with girls, blue with boys. Unfortunately, there is no consensus of opinion on its origin.
According to Jean Heifetz, for centuries, all European children were dressed in blue because the color was associated with the Virgin Mary. The use of pink and blue emerged at the turn of the century, the rule being pink for boys, blue for girls. Since pink was a stronger color it was best suited for boys; blue was more delicate and dainty and best for girls. And in 1921, the Women's Institute for Domestic Science in Pennsylvania endorsed pink for boys, blue for girls. (When Blue Meant Yellow. pp. 20 -21)
One could argue that contemporary color symbolism confirms these associations. Blue is considered a calm, passive color, hence feminine. Red (pink derived from red) is considered active hence masculine.
On the other hand, the idea of associating blue with male babies may stem back to ancient times when having a boy was good luck. Blue, the color of the sky where gods and fates lived, held powers to ward off evil, so baby boys where dressed in blue. In Greece a blue eye is still thought to have powers to ward off evil. The idea of pink for girls might come from the European legend that baby girls were born inside delicate pink roses.
Another theory states that the sexual origins can be found in ancient China. At a time when certain dyes were quite rare, pink dye was readily available and therefore inexpensive. Since blues were rare and expensive, it was therefore considered to be more worthwhile to dress your son in blue, because when he married the family would receive a dowry."