In 1916, Infants' and Children's Wear Review insisted upon pink for boys and blue for girls. In 1939, Parents magazine claimed that pink was a good color for boys because it was a pale version of red, which was the color of Mars, the war god. Blue was good for girls because it was the color of Venus, and of the Virgin Mary. So, pink for girls is a relatively recent trend, and utterly random.
Tim Gunn, Tim Gunn's Fashion Bible: The Fascinating History of Everything in Your Closet
colors, fashion, gender-stereotypes