Practice with Munsell color charts

This color exercise in which I am working to discern and to control chroma precisely.  I wanted to mix accurately the red and green in the apple in the light and shadow sides. The shadow side is tricky because you want to maintain the correct hue but lower the value and chroma. 
There are three basic ways to reduce chroma — 
a) mix with a neutral (either black & white mixed, or, better, a complement-mixed neutral), 
b) mix with a complementary color
c) mix with a lower-chroma version of your color (often a brown or other earth color). You will have such lower chroma colors for only a few of your hues.