Additive Color Theory

White light is the sum of red, green and blue light. Black is the absence of color. Used for transmissive colors, i.e. light shines through an object. e. g. TV screen, Computer monitor, transparencies.Secondary colors are produced from two color overlap.

Blue + Green = Cyan

Red + Blue = Magenta

Green + Red = Yellow

Combining in unequal proportions yields new colors. Essentially all perceivable colors can be represented by different amounts of RGB. RGB is usually the native color model used by computers and is also used on most desktop scanners.

Subtractive Color Theory

Secondary colors are used as subtractive primaries, Cyan, Magenta and Yellow. Used when light is reflected from an object such as printed page or photograph. Pigments are examples of subtractive colors which reflect some wavelengths and absorb or subtract others. Cyan pigment absorbs Red and reflects Green and Blue, i.e. appears cyan. Magenta pigment absorbs Green and reflects red and blue, i.e. appears magenta.

Yellow pigment absorbs blue and reflects red and green, i.e. appears yellow. When subtractive primaries are overprinted you get Red, Green and Blue (RGB). The subtractive primaries (CMY) can be thought of as the complements of R, G and B respectively.

Cyan + Yellow = Green

Cyan + Magenta = Blue

Magenta + Yellow = Red

Cyan + Magenta + Yellow = Black

These all assume ideal pigments which are exact complements of the human perceived Red Green and Blue. Then all colors represented as RGB can also be represented by CMY. The subtractive color theory and the associated CMY pigments form the basis for color printing. However, real CMY pigments only approximate ideality. Thus, there are some colors which can be displayed using RGB that cannot be printed.