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]
[1910s+] (US black)

1. a white person.

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