[sassbox]

during her earthly life she probably never wore anything blue, since she was poor and dyes were expensive. It is a lovely color though!

[HarleyD]

I don't think the color blue in classical paintings had to do with realism. I believe it represented something (purity, holiness, etc.). It has been many years since I've studied art. Perhaps an art major would know.

It's not important. This looks like a neoclassical painting to me and I thought most neoclassical painters painted Mary's robed in blue. (see below some examples)