We drew out our composition lightly in pencil together. Near the end of this, I told students they could add elements to their drawing if they had big, empty spaces.
We started the coloring with yellow. I asked them to color 2 or 3 parts of each thing yellow, then they colored 1 or 2 parts red, followed by a part or 2 blue. We got mixing at that point. The kids got a kick out of seeing how the colors changed.
At the end of the lesson, I posted 3 sentences about color mixing that they could choose from for their exit sentence. We read them aloud together and they chose one to write.