After much experience with mixing the primary colors, I introduced this activity as a way to use those skills and introduce the order and colors of a rainbow.
The tray contains the needed materials (except a small jar of water for painting). A child using this activity should know the names of primary and secondary colors, how to mix primary colors to make secondary colors, how to use a dropper and watercolors and be able to follow through with clean-up.
On the tray I included a picture of a real rainbow for reference.
I also drew a rainbow to clearly demonstrate the order of the colors. The plastic bag keeps it from getting wet and extra papers are also kept inside.
We also use a work mat (laminated piece of paper in this case) for art activities. We started by looking at the photo and then naming the colors of the rainbow in order using the drawing.
Using the dropper, the primary colors were each put into an ice-cube square. New colors were made by following the cards and mixing the primary colors. The dropper is wiped on the sponge after each use.
After the color mixing is complete, a rainbow can be painted.