Confirming Cecil’s answer to the ‘pink for girls’ question, that it is not a longstanding and universal tradition: I can attest that in the St Pierre/St Pieters Hospital in Brussels (affiliated with the ‘Universite Libre de Bruxelles’) the colour of the files in the paediatric department -at least as late as the 1990’s- was pink for boys and blue for girls.
Link to column in question: http://www.straightdope.com/columns/read/2831/was-pink-originally-the-color-for-boys-and-blue-for-girls
The obvious candidate would be the rise of the women’s rights movement, surely? Votes for women, suffragettes throwing themselves under horses and suchlike?
Perhaps people, consciously or not, then felt an urge to more strongly delineate gender differences?
I am guessing the two trends are connected, but others are implicated, as well. (Freudian psychology, social Darwinism, and consumer culture) This article is based on an interview done as I was finishing the research for my book Pink and Blue (2012), so it is somewhat preliminary!
I have written about this here as well.