First we divided up our canvases into geometric shapes using masking tape. Then we painted in the exposed spaces with acrylic paint. Oh, one more rule: we used only the three primaries. Any other colors had to be mixed.
We practiced first - we filled in color wheels by mixing the primaries, secondaries, and analogous colors. This is an excellent exercise, by the way, which can and should be done with kinders on up (start with simpler color wheels with younger children using only the primaries and secondaries).
Many of our young artists decided that complementary colors look really awesome together, meaning colors that are opposite one another on the color wheel. Others preferred analogous colors: those that touch or nearly touch on the color wheel, such as cool colors (blues, violets, greens) or warm colors (yellow, reds, and oranges).
After the paint was completely dry, we removed the tape and - WOW!