Green’s Dictionary of Slang

kelt n.

also kelch, kelsey, keltch, keltz
[? Scot. kelt, a homespun cloth, usu. of black and white wool mixed, once used for outer garments by country people]
(US black)

1. a white person.

[UK]F.M. Hueffer Panel I. i. 14: ‘Do you mean to say that you haven’t got a single book of James’?’ ‘Never heard the name,’ the bookstall boy said. ‘But there’s plenty by Mrs. Kerr Howe.’ ‘That kelch!’ Major Foster exclaimed [OED].
[US]C. McKay Banjo 103: ‘What a saucy-looking doll that one is!’ Banjo exclaimed. ‘I ain’t studying any kelts,’ replied Taloufa. [Ibid.] 107: I ain’t got any appreciation at all for the kelts.
[US]Monteleone Criminal Sl. (rev. edn).

2. used to mean a light-skinned black person, in phr. such as three-quarter kelt.

Eve. Sun (Baltimore, MD) 9 Dec. 31/5: Three-quarter kelt — a mulatto.
[US]J.L. Kuethe ‘Prison Parlance’ in AS IX:1 27: three-quarter kelt. A light-skinned Negro.
[US]C. Himes ‘Pork Chop Paradise’ in Coll. Stories (1990) 265: Then he met a high-yellah gal, a three-quarter keltz, from down Harlem way, and she sent him to the dogs.