RGB is an abbreviation for red, green, and blue, the primary additive colors. Computer monitors, televisions, and digital cameras use RGB color. Mixing red and green light makes yellow, green and blue makes cyan, and blue and red makes magenta. Mixing all three makes white.

The red, green, and blue primaries can be thought of as axes which form a three-dimensional cube. Inside that cube is every color that can be represented in RGB.

The inside and outside of an RGB cube. Every point inside the cube is a unique color, however this illustration only shows those on the surface.

Computers represent color in RGB, typically as three numbers ranging from 0–255 (the range of a byte). Three bytes, one for each channel, can represent over 16 million colors. This is known as 24-bit color, 32-bit color, or true color. RGB is used because it corresponds directly with the three phosphor colors in a computer monitor. Phosphors are tiny patches of a substance which glows briefly when struck by the electron beam at the rear of a monitor. Each pixel on the screen consists of three side-by-side red, green, and blue phosphors. Varying the brightness of each phosphor in a pixel changes its color. The following simulation shows what a computer screen looks like. If you look at the illustration closely you'll see bands of red, green, and blue at different intensities. If you sit back a bit you'll see a color picture.

Simulation of how a television or computer screen's red, green, and blue phosphor colors can display a color image.

A 4x magnification of the same picture. (These images are 1/3 as bright as on a normal screen due to the nature of the simulation.)

RGB is device dependent, meaning that a color described in RGB will look different on different monitors. Every monitor has its own brightness, color purity, and gamma. sRGB was introduced to solve this problem. sRGB stands for standard RGB and was proposed by W3C to standardize color on the world wide web. It works exactly the same way as RGB and is more a standard for how to use RGB than an entirely different color model. For instance, the sRGB standard assumes a monitor gamma of 2.2. If web designers use this standard for creating graphics and browser writers use this standard for displaying graphics, colors will be more accurate to what was intended when displayed on a user's screen.

Sample image: Detail of "The Anatomy Lecture of Dr. Nicolaes Tulp" painted by Rembrandt in 1632.