Slang : an attractive thing.
The paint stuff that makes the color, a.k.a pigment, is dissolved in oil, could be your mundane salad oil (edible vegetable oil is OK but you may prefer or a more technical liquid for a less shrimp brained look).
Oil pastel odor is better than expensive scientific investigations to determine when and how an oik picture was made.
Jan van Eyck, What are they thinking?