Until quite recently in the 20th century blue was the color for dressing girls and pink for dressing boys.
This painting by Renoir is of a boy not a girl:
The Sunday Sentinel, March 1914, noted: "use pink for the boy and blue for the girl, if you are a follower of convention."
In June 1918, the US magazine Ladies' Home Journal wrote that despite some confusion "... 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."
Even as late as 1927 there was ambivalence on the subject. Time magazine reported that Princess Astrid of Belgium had decked out the cradle for her unborn child in pink, only to give birth to a
daughter. The correspondent decided to run a straw poll among U.S. department stores but found they could not agree which way it should be either.
Note Gainsborough's 'Boy In Blue':
Source - BBC History magazine
I remember a western movie in which Burt lancaster, or is it Robert Mitchum, is caught in flagrante delicto in a woman's bedroom and he escapes through the window in pink, whole body button-up underwear.