An Etymological Dictionary of the German Language/Annotated/blau
blau, adjective, from the equivalent Middle High German blâ (Gen. blâwes), Old High German blâo, ‘blue’; compare Dutch blaauw, Anglo-Saxon blâw, and with a suffix blœ̂wen; English blue (from Middle English blew) is borrowed from French bleu, which, with its Romance cognates (Italian biavo, from *blawo), is of German origin. The primitively cognate Latin flâvus, ‘flaxen, yellow,’ has, like so many names of colours, changed its meaning compared with the German word.