The dark rim round the eyes after much weeping. A peculiar appearance in a rainbow which indicates more rain at hand. “Gall” is the Anglo-Saxon gealew (yellow).
And round about her tear-distainëd eye Blue circles streamed, like rainbows in the sky; These watergalls ... foretell new storms.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894