Brewer's: Blue Ribbon
(A). A wale from a blow. A bruise turns the skin blue.
“ `Do you want a blue ribbon round those white sides of yours, you monkey?' answered Orestes; `because, if you do, the hippopotamus hide hangs ready outside.' ” —Wingsley: Hypatia, chap. iv.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894