Internet slang used by drug dealers and users alike to denote cocaine use.
I have some white paint, if anyone is interested. Private message me, for details.
Painting is usually used to denote bodily fluid emitted onto another person during gay sex. Brown paint denotes when a penis has come out of the anal cavity with fecal matter all over it, so white paint denotes when the penis ejaculates all over the partner with semen, painting them "white."
I have some white paint for your face, if you want any of it.