Here, courtesy of my son, whose interests are as wide-ranging as they are eccentric, is historical evidence that social constructs are more fluid than we might suspect.
He found an article in Smithsonian magazine that answers the question: "When did girls start wearing pink?"
It seems that, baby girls have been swathed in pink only since World War Two. Prior to that, the custom was to put boys in pink clothes and girls in blue.
A 1918 article in the Ladies Home Journal advised, “The generally accepted rule is pink for the boys, and blue for the girls. The reason is that pink, being a more decided and stronger color, is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl.”
But even that practice dated from just before World War One. Before that, babies of both sexes were put in white dresses -- and they stayed there until they were five or six -- because white clothes could be bleached clean.
Using colors to mark gender was made possible by the invention of modern detergents. The article doesn't try to explain why pink and blue emerged as the generally accepted markers or why the significance of the colors flipped in the early 40s.
But pink and blue have been gender markers for more than a century, except for a period beginning in the 1960s when the rise of feminism prompted moms to put their kids in neutral unisex clothes.
That lasted until around 1985, when pre-natal testing started giving parents advance word of their baby's sex. (And all those little girls who had been put in unisex clothes were having babies of their own and decided to dump the unisex look.)
So we could do it again. Or maybe change some other social construct that has more significance and a higher cost.