I don't know how it became a feminine colour, but in the eighteenth and nineteenth centuries pink was a colour for boys.

In the US, it seems to have come from France. 1) "In Western culture, the practice of assigning pink to an individual gender began in the 1920s. From then until the 1940s, pink was considered appropriate for boys because it was the more masculine and decided color while blue was considered appropriate for girls because it was the more delicate and dainty color. Since the 1940s, the societal norm apparently inverted so that pink became appropriate for girls and blue appropriate for boys, a practice that has continued into the 21st century." "It has been suggested that females prefer pink because of an evolutionary preference for reddish things like ripe fruits and healthy faces. This suggestion, however, has been criticized as unsubstantiated." Source and further information: http://en.wikipedia.org/wiki/Pink#Pink_in_gender 2) "Girls had more dolls, fictional characters, child's furniture, and other toys for manipulation. They wore pink and multicolored clothes more often, had more pink pacifiers and jewelry. Boys wore more blue, red and white clothing. They had more blue pacifiers. Yellow bedding was more frequently observed in the girls' rooms, while blue bedding and curtains were more prevalent in the boys' rooms. Women were the predominant providers of toys for children. It thus seems that, nowadays, very early in their development, girls and boys already experience environments which are dissimilar." Source: http://www.springerlink.com/content/w77382423043083r/ 3) "when the women were asked to choose from mixed colors, they tended to prefer colors that moved away from blue and toward the red end of the spectrum, where shades like pinks and lilacs are found. The scientists concluded that the long-held distinction of color preferences among genders had a real basis." " The results were similar among the Chinese women and the British women: Both preferred the shades found on the red side of the spectrum. This lends support to the notion that color preferences among the sexes have a biological basis rather than a cultural one." "The Princeton group posits that kids become aware by age two that there are two distinct genders and that they belong to one of them. Securing a place in one's gender is important to a child's psychological development. One easy way for a child to achieve this security is by adopting the color assigned to his gender by society and rejecting the other" "Since the Princeton study suggests a combination of both biology and culture is at work in color preferences, the question still remains: Is biology or culture responsible -- or both?" Source and further information: http://people.howstuffworks.com/gender-color.htm 4) "The practice of pink for girls and blue for boys was introduced into the United States from France in the mid-19th century; in Little Women, Amy tied a pink ribbon on Daisy, and a blue one on her twin, Demi, "French-style, so you can always tell." But the practice was not common until after World War II, partly because there was considerable disagreement about which color was appropriate for which sex. The Infant's Department, a trade journal, tried to settle the question in 1918: "There has been a great diversity of opinion on the 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 a boy, while blue, which is more delicate and dainty, is prettier for the girl." Clothing manufacturers complained that greeting-card companies were confusing the issue by using pink for girls and blue for boys in birth announcements. The greeting-card people pointed to Gainsborough's "Blue Boy" and "Pinky" as proof they were right. The debate continued for decades. in 1939, Parents magazine polled customers in a New York department store and found that, while most preferred pink for girls, about one-fifth favored blue for girls and pink for boys. The first children to be consistently color-coded by gender were the post-war baby boomers. Pink has been an exclusively feminine color for only about 40 years. (This explains all the sweet, elderly ladies who thought your son was a girl even when he was dressed all in blue.)" Source and further information: http://www.gentlebirth.org/archives/pinkblue.html Further information: Boys like blue, girls like pink - it's in our genes: http://news.independent.co.uk/sci_tech/article2881412.ece Genes make men prefer blue, women pink: http://www.dancewithshadows.com/society/genes-sex-color.asp Women really do prefer pink, researchers say: http://www.reuters.com/article/scienceNews/idUSL2081187520070820 Pink -- why feminine? http://answers.google.com/answers/threadview?id=238733 Color and Gender: http://histclo.com/gender/color.html Pink, pink, pink, pink. Pink moan: http://www.badscience.net/?p=518

cause someone decided to make it that way

Because it is Barbie's signature color.