it started earlier than that....from an article - http://www.todayifoundout.com/index.php/2014/10/pink-used-common-color-boys-blue-girls/
In 1927, Time magazine printed a chart highlighting gender-appropriate colors for girls and boys according to leading U.S. retailers. Filene’s (in Boston), Best & Co. (in New York City), Halle’s (in Cleveland), and Marshall Field (in Chicago) all advised parents to dress boys in pink and girls in blue. Why did they care at all? It is generally thought it was simply because if parents followed such a color scheme, they would have to buy a whole new wardrobe and set of baby accessories in the “appropriate” colors if they had a boy and a girl at some point, rather than just going with reusing the one set for both as before.
For reasons unknown, this all started to change around the 1940s when clothing manufacturers decided on pink for girls and blue for boys. It has been suggested that boys simply like blue more and girls like pink more, but studies to date trying to see if this is true have come up with mixed results, except firmly showing that the vast majority of humans prefer blue to pink, and pink is actually one of the adult world’s least favorite colors. (As you might imagine, it’s difficult to perform large scale studies to determine if boys and girls are naturally predisposed to one color or another without the introduction of existing learned color biases, even in countries that don’t popularly follow the pink-girl/blue-boy scheme.)