Aha! Finally, an explanation that makes sense:
Just as boys were once clothed in dresses, they were also once swaddled in pink. Historically, in many European countries, pink was the dominant color for boys, and blue—the official hue of the Virgin Mary—was the popular girls’ color. (emphasis mine)
which appears in an article by Brian Palmer at Slate about gendered clothing for young children, and whether or not Shiloh isn’t just a trendsetter (or retro, depending).
(Which forces me to admit: I was surprised the author of the article is male. Ah, gendered expectations always bite in the end.)