Green’s Dictionary of Slang

(US black) skin; also adj.

1946		D. Hill ‘Chalky’ in Lehmann Penguin New Writing No. 28 173: There he was, the black-enamelled bastard.
1946		Mezzrow & Wolfe Really the Blues 204: The star strip-teaser would come out on the runway, unwrap her enamel, and then begin grinding the ozone.