''PINK for girls, BLUE for boys'': See how it all started

Blue is for boys and pink is for girls, we're told. But do these gender norms reflect some inherent biological difference between the sexes, are there gender-color symbolism that held true anywhere,or are they culturally constructed? It depends on whom you ask.

Baby books, new baby announcements and cards, gift lists and newspaper articles from the early 1900s indicate that pink was just as likely to be associated with boy babies as with girl babies. For example, the June 1918 issue of the Infant's Department, a trade magazine for baby clothes manufacturers, said: "There has been a great diversity of opinion on this subject, but the generally accepted rule is pink for the boy and blue for the girl. 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 this attempt at establishing the rule for retailers and manufacturers clearly did not stick. 

As for why today's strict color-gender norms set in at all, Philip Cohen, a sociologist also at the University of Maryland, thinks they are, essentially, the outcome of a marketing ploy.

"This happened during a time when mass marketing was appearing," Cohen told Life's Little Mysteries. "Being 'gender normal'' is very important to us, and as a marketing technique, if retailers can convince you that being gender normal means you need to buy a certain product — cosmetics, plastic surgery, blue or pink clothing, etc. — it just makes sense from a production or mass marketing perspective," Cohen wrote in an email.

As for why one color-gender pairing came to dominate over the opposite pairing, Paoletti argues that the rule we use today may reflect the influence of French fashion. Traditional French culture paired pink with girls and blue with boys (while Belgian and Catholic German culture used the opposite), and because France set the fashion in the 20th century, their tradition held sway.

However, a new letter published July 21 in the Archives of Sexual Behavior questions this widely accepted pink-for-girls, blue-for-boys origin story.