Shades of magenta yellow and cyan, constitute the three subtractive primary colors of pigment. (The secondary colors of pigment are blue, green, and red.) As such, the CMYK printing process was invented in the 1890s, when newspapers began to publish color comic strips. Process magenta is not an RGB color, and there is no fixed conversion from CMYK primaries to RGB. Different formulations are used for printer's ink, so there can be variations in the printed color that is pure magenta ink. A typical formulation of "process magenta" is shown in the color box at right. The source of the color shown at
RG color space replicated accurately in the RG color space. There is a similar color space called RGK which 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, where red and green tended to be far more common than the still nascent blue LED technology, though full-color LEDs with blue have become more common in recent years. ColorCode 3-D, a stereoscopic color