The Color Wheel . By Don Finkeldei:  This is pretty basic stuff  for experienced painters -- but -- you cannot be an experienced painter without nowing this.

The Color Wheel:

The wheel is arranged with yellow, the lightest value color at the top and violet, the darkest value color at the bottom. From the top down on the right are yellow-orange, orange, red-orange, red, and red-violet. These are called the warm colors. From the top down on the left are yellow-green, green, blue-green, blue and blue-violet. These are called the cool colors.

Complementary Colors:

Any TWO colors directly across the color wheel from each other are called COMPLEMENTARY COLORS. Red and green are opposite each other on the color wheel and therefore are complementary to each other. Yellow and violet are each other's complements. Yellow-green and red-violet are complements. Complimentary colors when placed next to each other on the canvas intensify each other. Complementary colors when mixed together on the palette neutralize each other. In this chart the pure intense colors are on the outside opposite their complements. As we move to the middle, the complements are mixed together until they become gray, the least intense of all.

 Color Values:

 All colors come in all values. The pure spectrum colors are in the position of their relative values on this seven-value scale.  With These Things in Mind, This is How to Match Any Color.  We have only to answer these three questions to match any color we see.

1. WHAT COLOR IS IT FROM THE COLOR WHEEL? (Its spectrum color)
2. HOW INTENSE IS IT? (How much of its complement does it contain? More complement means less intense.)
3. WHAT VALUE IS IT? How light or dark is it?