The Forest Republican, Tionesta, Pennsylvania, July 3, 1889

Dollar Weekly News, Wilkes-Barre, Pennsylvania, November 15, 1890

Harrisburg Telegraph, Pennsylvania, November 17, 1890

The Times, Philadelphia, May 7, 1901

The Evening World, New York, July 19, 1905

Chicago Daily Tribune, June 2, 1914

The Baltimore Sun, Maryland, August 22, 1916

The Morning News, Wilmington, Delaware, June 23, 1919

The News-Review, Roseburg, Oregon, November 16, 1929

I don’t know if anyone else has come across this, but I’ve read a lot of articles (Mental Floss, Jezebel, Smithsonian, NPR) that seem to conclude that while the colours could be interchanged and it wasn’t quite settled (I agree), the colour pink was more commonly a boy’s colour, while blue was for girls, until WWII. Almost all articles quote one single trade journal from 1918: 

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 from what I can find, while there’s some wiggle room - a couple articles I found said pink could certainly be used for boys - for the most part it’s generally been “pink for girls” and “blue for boys” since at least the 1890s. “Pink was a boys colour” seems like a bit of a modern myth perpetuated by that one source.