RG color space

The RG or red–green color space is a color space that uses only two colors: red and green. It is an additive format similar to the RGB color model but without a blue channel. Thus, blue is said to be out of gamut. The format is not in use today, and was used only on two-color Technicolor and other early color processes for films. By comparison with a full spectrum, its poor color reproduction made it undesirable. The system cannot create white naturally, and many colors are distorted.

The additive RG color space can produce shades of black, red, green, and yellow.

The subtractive RG color space can produce shades of transparent (not white), red, green, and black.

No color containing a blue color component can be replicated accurately in the RG color space. A similar color space, called RGK, also has a black channel. Outside of a few low-cost high-volume applications, such as packaging and labelling, RG and RGK are no longer in use because devices providing larger gamuts such as RGB and CMYK are in widespread use. Until recently, its primary use was in low-cost light-emitting diode displays in which red and green tended to be far more common than the still nascent blue LED technology, but full-color LEDs with blue have become more common in recent years.

ColorCode 3-D, a stereoscopic color scheme, uses the RG color space to simulate a broad spectrum of color in one eye. The blue portion of the spectrum transmits a black-and-white (black-and-blue) image to the other eye to give depth perception.

Additive RG	Additive RG color palette