Color mixing
There are two types of color mixing: Additive and Subtractive. In both cases there are three primary colors, three secondary colors (colors made from 2 of the three primary colors in equal amounts), and one tertiary color made from all three primary colors. This point is a common source of confusion, as there are different sets of primary colors depending on whether you are working with additive or subtractive mixing.
Additive Mixing
The additive mixing of colors is unintuitive as it does not correspond to the mixing of physical substances (such as paint) which would correspond to subtractive mixing. For instance, one can additively mix yellow and blue by shining yellow light together with blue light, which will result in not green but a pinkish light. As in this example, one should always have the mixture of light in mind when considering additive color mixing as it is the only situation where it occurs. Despite being unintuitive, it is conceptually simpler than subtractive mixing. Two beams of light that are superimposed correspond to additive mixing.