In theory, mixing all colors in equal proportions would produce black, using the subtractive method of color combination. In the additive method, the same approach produces white.
Red, green and blue are used for additive coloring, while cyan, magenta and yellow are used for subtractive coloring. The subtractive approach, which involves mixing pigments rather than mixing beams of light, gradually introduces pigments that preferentially absorb, or "subtract," certain wavelengths of visible light. A balanced combination of the three primary colors absorbs all wavelengths of visible light, leaving only black. In practice, however, this method is difficult to achieve perfectly, and many black pigments are slightly shaded blue or red.