Violets are blue?

The old rhyme we used to write in each other's autograph albums proclaims that "Roses are red, violets are blue . . . .". I suppose rhyming would have been difficult if they had said "violets are mauve"! But mauve they definitely are, not blue.
As children we were sent home from Sunday School with a bunch of violets to give to our mothers on Mothering Sunday. How times change.