Green’s Dictionary of Slang

black-assed peas n.

[the colouring of the legume]

(US black) soul food, esp. black-eyed peas.

1979		in DARE.
1994		(ref. to 1940s–70s) C. Major Juba to Jive 38: Black-assed pea n. (1940s–70s) Black-eyed peas.