One of the first exercises that Gail Sauter had us do in her painting workshop was color mixing studies with the palette knife. It was an interesting and fun way to see the possible combinations of colors you could achieve by simply mixing 2 or 3 colors together with white. I still have them and refer to them occasionally as I paint now.
These first 2 images show mixing just 2 colors with white. These are only about 4" by 4" each, but look at the beautiful possibilities! One side shows the warmer range, the other shows the cooler range. Can you see which is which?
And here are some using 3 colors and white. Using the same three colors, you can see the warm colors created on the left and the cools on the right.
And this was a little study about using the opposite temperature to make your subject stand out. For instance, the left side shows a cool subject against a warmer background. The right side shows a warmer subject against a cooler background.
Fun! Just looking at these again makes me want to do more.