Interesting enough, white was the universal color of infants and young children alike prior to WWI. The fashion decision was actually quite practical. White could be cleaned with bleach and well, kids are messy.
When retailers first began promoting infant merchandise by color, blue and pink were used equally for both genders before shifting to gender specific colors. However, it did not kick off as you would guess. According to smithonian.com:
Ladies’ Home Journal article in June 1918 said, “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.”
Over time, the colors were reversed by the retail industry to the pink for girls and blue for boys that we have today. Even so, the trend didn’t truly take off until the 80’s!