mullion, n. — Green’s Dictionary of Slang

mullion n.

[? SE melungeon, a member of a racially mixed group of people – half black, half Native American – centred in the Appalachians, ult. Fr. mélange, mixture]

(US black) an unattractive woman or ugly person.

1960		J. Brosnan Long Season (1975) 247: ‘Hey, Mullion-man!’ Lawrence said to Daniels and they both grinned [...] ‘But what does it mean?’ ‘Like, not pretty. You know. Ugly, you might say.’.
1972		D. Claerbaut Black Jargon in White America 73: mullion n. a physically unattractive person.
1977		Fidrych & Clark No Big Deal 193: I’m rappin’ to a nice chick, and all of a sudden this mullion chick comes up and says, I want a date.