A primary color can be created through no combination of other colors. In emissive light they consist of the following:
(There are also the primary pigments, which refer to reflected color.)
The color of light is said to be additive. different colors are created as you mix them. As you add together equal proportions of primary colors, you approach white. Conversely, the absence of color in light is black.
This is the reason that television uses red, green, and blue phosphors. Any color combination can be represented by mixing different proportions of the primary colors. Note that in practice this is restricted by technical limitations of the medium, for example the television standard NTSC is noted for its inability to represent certain colors to retain backward compatibility with black and white televisions.
For a more detailed and extensive treatment of color, see color.