Yellow is the color evoked by light that stimulates both the L and M (long and medium wavelength) cone cells of the retina about equally, but does not significantly stimulate the S (short-wavelength) cone cells; that is, light with much red and green but not very much blue. Light with a wavelength of 570–580 nm is yellow, as is light with a suitable mixture of somewhat longer and shorter wavelengths. Yellow’s traditional RYB complementary color is purple, violet or indigo. Yellow’s colorimetrically defined complementary color in both RGB.
Process yellow (also known as pigment yellow, printer’s yellow or canary yellow) is one of the three colors typically used as subtractive primary colors, along with magenta and cyan. The CMYK system for color printing is based on using four inks, one of which is a yellow color. This is in itself a standard color, and a fairly narrow range of yellow inks or pigments are used. Process yellow is based on a colorant that reflects the preponderance of red and green light, and absorbs most blue light, as in the reflectance spectra shown in the figure on the lower right.
Because of the characteristics of paint pigments and use of different color wheels, painters traditionally regard the complement of yellow as the color indigo or blue-violet.
Process yellow 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 yellow ink.
and CMYK color spaces is blue.
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