'Blue for a boy; pink for a girl' is a comparatively modern idea. Its firm use probably dates from the early decades of the twentieth century, and has been encouraged by producers of greetings cards and baby books.

It all seems to begin with blue, which has been associated with sky spirits and regarded as a protective colour from ancient times. Its use as an amulet could be extended to any prized asset, such as one's boat, or horse, as well as to humans. In many cultures, women often did inherit businesses or estates, but male heirs were preferred for strength and for preserving family identity. There seems also to be some evidence that male babies may be biologically weaker than the females, so more in need of protection.

But in those communities which are predominantly Roman Catholic, blue is a colour which is associated with the Virgin Mary, and so was often thought more appropriate for girls. Pink was then used to designate boys: it can be linked with red, which is sometimes associated with St Joseph. The pagan version of this is a European legend about birth: boys come from under blue cabbages and girls from inside pink roses. Pink for boys and blue for girls was also found in the UK, and although blue for boys and pink for girls was gaining in popularity during the 19th century, the Women's Institute were still issuing booklets recommending pink for boys and blue for girls as late as 1921.