E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Moslem soldiers. The banner of the Abbasides (3 syl.) is black; that of the Fatimites (3 syl.) green; and that of the Ommiades (3 syl.) white. Hence the banner of the Kalif of Bagdad is black, but that of the Sultan of Damascus is green. (Gibbon, chap, iii.)
Black Flags. Pirates of the Chinese Sea who opposed the French in Tonquin, etc.