Kandinsky's expressionist paintings are always a great avenue for a fun lesson on color.
I brought a big poster of his, "Concentric Circles", and talked briefly about the colors Kandinsky used in his painting: mostly tertiary colors, tints and shades of these.
I showed everyone how to mix primary and secondary colors to get tertiary colors (what most 3rd graders learn about), and then talked about how to make tints and shades. I didn't want to make too many guidelines for this project because painting with lots of color, and painting loose circles in the style that Kandinsky worked, yields for the kids to enjoy their discoveries while mixing colors, and the process of the experience. I was super happy to see the students feeling gutsy enough, confident enough to deviate from the example of Kandinsky's work and use more monochromatic color schemes, or using mostly tints, some have only warm colors and cool colors. Below are some awesome examples. (Click to enlarge)