When I was in figure painting class in college, my professor pointed out to me the different colors where the light hit models black, straight hair. It was like the Wizard of Oz when everything went from black and white to color. I then trained my eye to see color everywhere!
Since then, I've translated "gray" shadows as beautiful little rainbows, "green" trees as a palette of blues and yellows, and "skin color" as lavendars, blues, pinks and yellows.
Straight Out of the Tube
What didn't make sense to me was when I was told to never use the color straight out of the tube. Being the rebel that I was, I not only used color right out of the tube, but I rarely mixed my colors. When I painted with watercolor, I let them blend on the paper with the spontaneity of the water, rather than blending on the palette.
Now that I paint with oils, I still don't mix colors much on my palette. Mixing colors mutes them a little. Also, since I paint alla prima, the color get blended on the canvas naturally. If you like the color in my paintings, here are the simple recipes for my favorite colors.