RG color models
An RG color model is a dichromatic color model represented by red and green primary colors. The name of the pair of models comes from the initials of the two primary colors: red and green. The model may be either additive or subtractive. The primaries are added together in varying proportions to reproduce a linear gamut of colors, which can reproduce only a fraction of the colors possible with a trichromatic color space, such as for human color vision. The appearance of the color gamut changes depending on the primary colors chosen. When the primaries are complementary colors (e.g. red and cyan), then an equal mixture of the primaries will yield a neutral color (gray or white). However, when the primaries are not complementary colors, an equal mixture of the primaries will yield yellow, and a neutral color cannot be reproduced by the color space. Despite its shortcomings in color reproduction, these models were used in early color processes for films. (Wikipedia).
