All ages LOVE color mixing with water and food coloring! I always begin with red, yellow and blue, leaving a jar of clear water between the primaries. Kindergarten students were particularly awed when secondary colors "magically" appeared as we mixed the primary colors. Inspired by our color mixing, young artists then drew their own rainbow art! (I snapped a couple of photos before sending them home...)
Wouldn't it be nice if unicorns really did climb rainbows?