Color matching is a great study you can do to examine the subtle shades in the world you see. you might call a stone gray, but when you get down to the real story it´s probably a soft shade of blue. And that purple stone... well it´s a very specific shade of mahogany plum if you ask me.
Apply your discoveries to larger works and paintings. You might use the blues you discovered in a mountainside or riverbed.
STEP 1 - Choose something that catches your eye, from a special moment, something meaningful. I chose stones from the Snake river because they mesmerized and fascinated me. I mean, I really couldn't get over the variations and violet hues. The peach and soft blues together were so warm.
STEP 2 - Get out a glass plate, brushes, and a cup of water. Mix your watercolors. Avoid the black. Put the black away. If you need a dark color, or to gray something add its complementary. Orange and blue, red and green, or yellow and purple. Those are the compleementary colors, and your key to getting colors you see in the world.
For a fun exercise try picking up some blocks, dog toys, or highlighters. Try matching those and see what happens. Pay attention to shadows and highlights, those will be different. Add water to lighten pigments. Use gouache as an alternative, or throw in some whitened ashes from the campfire into your watercolors.