Green’s Dictionary of Slang

1. amphetamines.

1967		M. Braly On the Yard (2002) 285: It’s something like bennies — blancas — only not as good.
1993		L. Rodríguez Always Running (1996) 54: Pills they called colies or blancas (colies was short for coloradas, which meant ‘reds’ or downers; blancas stood for ‘whites’, uppers).
1995		in Stavsky, Mozeson & Mozeson A–Z.

2. cocaine.

2001

ONDCP Street Terms 3: Blanca (Spanish) — Cocaine.