This was a super simple activity, and it turned out great! All you need is a paper bowl (works best if it has a smooth bottom without varying heights or ridges,) green and blue paint, and black paper.
Flip your bowl upside down so the bottom is facing up (like a drum.) Sporadically place large dots of paint on the top (of the bottom) of the bowl. Then take your bowl, flip it over, and press it onto a scrap paper (like a big stamp) to make sure the entire surface is covered and you have enough paint. Then you are ready to press it onto your black paper (no new paint required!)