To dirty paint is to have a blank canvas i.e a very pale wench.
(Dirty painting is to try to make an improvement to an abomination of a woman which cant look any worse)
This act of dirty painting is when a fugly white girl is stripped down and have faecal matter from the artist rubbed all over the canvas. The artist may or may not choose to use a variation of bodily fluids for different colours. As in phlegm used for a green or a pale yellow, ear wax for orange, or spooge used for a white or a slimy texture. The dirty painting is only complete when the surface area of the wench is covered in exotic bodily fluids.
Guy 1: Did you hear about Wendy?
Guy 2: That disgustingly overweight blob that constantly smells like sweaty flab flaps?
Guy 1: Yeah! i heard some sick artist pinned her down and made her a dirty painting!?!?!?!
Guy 2: hope he made an improvement