I put together this worksheet after seeing one similar on Pinterest (I will site the original post when I find it again). The kids seem to have enjoyed doing this a lot more than I thought they might - and it makes for a great assessment piece.
*Tip: instead of using plastic mixing palettes, use scraps of cardboard. The students who finished early then can go on to create a mini painting on their palette!
This version I adjusted for my younger students by having a simpler image for them to paint.