That cute picture is of toddler FDR in a dress, from 1884. Jeanne Maglaty writes:
A Ladies’ Home Journal article [or maybe from a different source, according to a commenter] 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.” Other sources said blue was flattering for blonds, pink for brunettes; or blue was for blue-eyed babies, pink for brown-eyed babies, according to Paoletti.
In 1927, Time magazine printed a chart showing sex-appropriate colors for girls and boys according to leading U.S. stores. In Boston, Filene’s told parents to dress boys in pink. So did Best & Co. in New York City, Halle’s in Cleveland and Marshall Field in Chicago.
Today’s color dictate wasn’t established until the 1940s . . .
When the women’s liberation movement arrived in the mid-1960s, with its anti-feminine, anti-fashion message, the unisex look became the rage . . . in the 1970s, the Sears, Roebuck catalog pictured no pink toddler clothing for two years. . . . Gender-neutral clothing remained popular until about 1985. . . .
Which reminds me of this delightfully ridiculous story.