There have been some new discoveries in the traditional primary/secondary color wheel since Sir Isaac Newton created the first color wheel. Painters had originally learned that red, yellow, and blue are the primary colors in pigment. But because of research in the area of color we find that the true primary colors of pigment, those that are the basis for all others and cannot be made from mixed color, are magenta, yellow, and cyan. From these primary colors the secondary colors red, blue-violet and green can be mixed from combinations of two primaries. The result when all three primaries are mixed is black.
Color that we see is the result of a part of the visible spectrum that is reflected. We see yellow because only that part of the spectrum is reflected. Black occurs because all the colors of the spectrum are absorbed rather than being reflected. There is the opposite result when all primaries are mixed in light.
This process is also called subtractive color mixing and it is used in pigment and in commercial printing processes. I want to thank Larry Woolf from General Atomics in San Diego for his research and information on light and color.