January 10th- Sacre Bleu!

The phrase sacre bleu probably came from a late middle age Marian oath referring to the colour blue. Effectively meaning "sacred blue" it most likely refers to the fact that the virgin Mary is often depicted in blue clothing (blue was a very expensive dye.) It may also be a corruption of the verbs sacrer, meaning to crown, anoint or champion and Dieu, meaning God. Either way, I was wondering why it was sacre bleu and not sacre vert or sacre jaune...