Uncertain. Either from Proto-Indo-European *ǵʰelh₃- (“green”), or from *bʰel-, *bʰl̥H- (“yellow”). *ǵʰ- > f- instead of the expected *h- is explained as being regular in some dialects. Cognates through the first etymon include holus and helvus; Ancient Greek χολή (kholḗ, “bile”) and χλωρός (khlōrós, “green”); and English yellow and gold.