* Wet on wet rainbows
Wet on wet painting is a staple in Waldorf education. It produces beautiful paintings with the colors all running/mixing together. To create a wet on wet rainbow painting, submerge a sheet of watercolor paper in water. Remove and wipe off the excess water with a sponge or towel so that it remains wet but not dripping. Then use watercolors to paint on the wet paper. Use a thick brush and primary colors to create arcs for your rainbow. Let the colors mix together as you paint.
-- from Earth*School "April Showers Bring May Flowers"