Color models explain how colors work, interact and how we replicate color. Additive and subtractive color models are an application of color theory.
Additive Color
Cameras, televisions, phones and computer monitors use the additive color model. The additive color model describes how light produces color. The additive colors are red, green and blue, or RGB. Additive color starts with black and adds red, green and blue light to produce the visible spectrum of colors. As more color is added, the result is lighter. When all three colors are combined equally, the result is white light.
On digital devices, a red, green or blue element is activated by an electrical charge causing them to glow. These elements are called sub-pixels. By combining the three colors, the desired hue is created in one pixel. The pixels are then formed like tiny mosaics to create a picture. Hence, the unit of measurement for a digital graphic is PPI (Pixels Per Inch).
Subtractive Color
In the subtractive color model, pigment is used to produce color using reflected light. This color model is used in printing, silk-screening, painting and other mediums that add pigment to a substrate. The subtractive colors are cyan, yellow, magenta and black, also known as CMYK. Subtractive color begins with white (paper) and ends with black; as color is added, the result is darker. Printers use cyan, magenta and yellow inks in various percentages to control the amount of red, green and blue light reflected from white paper. In theory, adding equal amounts of cyan, yellow and magenta will produce black, but in reality, the result is often a very muddy dark brown. To produce a true black, black pigment is added. Black is referred to as "K," or the key color, and is also used to add density.
On a piece of paper, cyan, magenta, yellow and black pigments are distributed by the print head in tints. A tint is a screen of tiny dots appearing as a percentage of one color. The overlapping dots create the illusion of a hue. The various tints are then printed in overlapping patterns to create a picture. Hence, the unit of measurement for a print graphic is DPI (Dots Per Inch).
When to Choose RGB vs CMYK
It is important to choose the correct color model at the beginning of the project to get the best results. If the final product is for print, remember to convert the color mode from RGB to CMYK. If the final product will only appears on a screen or monitor, keep the color mode as RGB.
Because additive colors use transmitted light, the colors appear much brighter and create a larger visible spectrum, producing millions of colors on a screen. Subtractive colors use reflected light, so they appear muted in contrast. Limited by the ink pigments and tints, a printer can only replicate several hundred thousand colors. Because of this, the RGB colors on a monitor do not always equally translate into CMYK colors when printed on paper or other substrates.
Use this graphic as a quick reference to important basics for choosing between additive and subtractive colors for your next project.