Songs in the Key of Art is called "The Red and Yellow Blues". Since I tried to coordinate a lesson for each grade with one of the Songs in the Key of Art before the assembly, the Red and Yellow Blues was an easy choice. The lesson is one I've used before with Kindergarten and it's always a lot of fun.
On day 1, we listened to the song to review the primary colors before the students were given tempera paint in each of the primary colors, plus white, and asked to paint whatever they wanted! Some went for nonobjective themes while others painted portraits, houses, whatever their little hearts desired.
On day 2, the students were given mosaic squares to glue to their paintings. the squares could be used to define or add details. By the way, bottled glue holds these on waaaay better than glue sticks.