This is a simple grid for practicing color mixing. Students can practice mixing primaries and complements to create incremental steps (instead of a gradient).
When explaining how to complete the grid, it helps to describe how much color to use in each box. For example: the first box will have 100% of the color on the left and 0% of the color on the right. The second box in that row will have 75/25%, third will have 50/50%, and so on.
I print this on cardstock and students use tempera paint to complete it. You could modify your paper choice for any media! I use this with Art 1, and it typically takes them about 2 hours to complete.