Green’s Dictionary of Slang

blanco n.

[Sp. blanco, white; some varieties of heroin are white, rather than the usual brown]

1. (US black) a white person; also as adj.

[US]P. Thomas Down These Mean Streets (1970) 104: I just watched paddies come down out of that office and make it. ‘Louie,’ I said, ‘ask the next blanco that comes down how the job hiring is.’.
[US]A. Rodriguez Spidertown (1994) 1: Only patos wear that shit [i.e. aftershave]. Is that wha’ thum blancos need t’ score some pussy?
[US]J. Stahl Plainclothes Naked (2002) 31: Along with the two twenties the blanco creep had given her, her count came to $320.

2. (drugs) heroin.

[US]J.B. Rosensweig Calo.
[US]ONDCP Street Terms 3: Blanco (Spanish) — Heroin.

3. (US drugs) cocaine.

[US]Post-Star (Glen Falls, NY) 3 Aug. 18/5: There are many slang terms for cocaine [...] big C, blanco, blast, [...] girl, heaven, Mama Coca, [...] pimp, she [...] toot, trains, stardust.