Green’s Dictionary of Slang

1. (US black, also vanilla malt) a white person, esp. a female.

1941		J. Smiley Hash House Lingo 6: The entrance of a good looking woman is heralded with vanilla.
1971		(con. 1930s–50s) D. Wells Night People 118: Vanilla malt. A white girl.
1988		(con. 1940s) C. Bram Hold Tight (1990) 158: All our people, honey. And all flavors [...] But mostly vanilla.

2. (US gay) non-penetrative sex: cuddling and mutual masturbation.

1998

R. Scott Rebecca’s Dict. of Queer Sl. 🌐 vanilla — non-leather or non-kinky sex or the people who have that kind of sex.