To work with color media like paint, pastels, ink, or wax (crayons!), it is important to know how those colors are described and how they can be mixed to create the incredible variety of color we see in the world around us.

The first thing to learn is the types of colors:  Primary, Secondary, and Tertiary.

Primary Colors:  The primary colors in the artist palate are RED, YELLOW and BLUE.  These are the colors you start with to make all other colors.  It is important to have pure, true color if you want to be able to predict the colors you will get when you mix them together.  If you have an impure primary color it will make all your combinations "muddy". If you mix all three colors in equal proportions you will get something close to black. What about Brown? This color is a little different because it is the color you get when you combine all three of the primary colors but the most common version of it has more yellow and red than it does blue.

Secondary Colors: The Secondary colors are Orange, Green, and Violet (or Purple).
These colors are created when you mix equal parts of two primary colors.
1 Red +1 Yellow = 2 Orange
1 Yellow + 1 Blue = 2 Green
1 Blue + 1 Red = 2 Violet
Remember in science class when you learned the color spectrum ROYGBIV? You will notice that they are in the same order because the basis is the same principal. However, indigo (I) is more of a tertiary color that is more blue than red because it is a combination of blue and violet.

Tertiary Colors: The Tertiary Colors are Red-Orange, Yellow-Orange, Yellow-Green, Green-Blue, Blue-Green, Blue-Violet (what is closest to indigo in ROYGBIV), and Violet-Red.
These colors are created when a primary color is mixed with a secondary color.
1 Red + 1 Orange = 2 Red Orange
1 Orange + 1 Yellow = 2 Yellow Orange
These are the colors that people begin to give more creative names, because not only are the names kind of boring, they get more and more cumbersome as the colors get mixed further.  This is where names like Aqua, or Teal replace the names like Green-Blue or Blue-Green.
 

When the colors are arranged in a straight-line continuum they are called a spectrum.
All these colors are usually arranged on a "wheel" with pie shaped sections for each color.  This allows a person to see at a glance how the spectrum feeds back into itself at the end of the spectrum.

So what is left?
Black, White, and Gray
When you study light in science you learn that white is all colors of light and black is the absence of light.  Paint and other media work by reflecting light at the viewer.  It is not possible to mix all the colors of paint and get white, or even to get black.  Most pallets come with a manufactured black because it is nearly impossible to achieve true "coal" black by mixing.  They also tend to include an opaque white.  These two colors are very important because you can mix them with your primary, secondary, tertiary and other colors to affect the Hue.

HUE is the relative bright/lightness or darkness of a color.  If you begin with white and add red you will pass through different "shades" of pink until you have pure red.  Then if you start with red you will pass though darker and darker shades like burgundy until you end up with black.  Monochromatic works of art focus on the use of the many hues of one color.