Appearing before the Guardian's motley crew: a lot are no oil paintings! (12)

I believe the answer is:

watercolours

'no oil paintings' is the definition.
(a different technique to oil painting)

I don't understand how the remainder of the clue works.

(Another definition for watercolours that I've seen is " Artists' paints".)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.