blue: [13] Colour terms are notoriously slippery things, and blue is a prime example. Its ultimate ancestor, Indo-European *bhlēwos, seems originally to have meant ‘yellow’ (it is the source of Latin flāvus ‘yellow’, from which English gets flavine ‘yellow dye’ [19]). But it later evolved via ‘white’ (Greek phalós ‘white’ is related) and ‘pale’ to ‘livid, the colour of bruised skin’ (Old Norse has blá ‘livid’).
English had the related blāw, but it did not survive, and the modern English word was borrowed from Old French bleu. This was descended from a Common Romance *blāvus, which in turn was acquired from prehistoric Germanic *blǣwaz (source also of German blau ‘blue’). => flavine
