Extract from QI -
The people who were traditionally dressed in pink and called girls were boys. Pink was considered the traditional colour for boys and blue for girls in the 19th century. In 1927, there was a report about Princess Astrid of Belgium who had decorated her son's room pink, only for her to give birth to a daughter. Part of the reason why blue may be seen as the traditional colour for girls is because the Virgin Mary is dressed in blue. Right until the mid-15th century, all children were referred to as girls, boys were called "knave girls" and girls were called "gay girls". The word "boy" originally meant "servant".