RGB (Red, Green, Blue)
A color system commonly used to display color in video systems, film recorders, and computer monitors.
Its counterpart for printed materials is the CMYK system (cyan, magenta, yellow, black).
RGB represents all colors as combinations of red, green and blue light. It is an additive system (like a light spectrum) so adding equal amounts of each color produces white and no colors produced black. CMYK is a subtractive (reflective) system in which the lack of color equals white.
Each color in the RGB system is also called a channel. A fourth channel (alpha channel) represents transparency and is used in making a transparent GIF. To display all three colors in one pixel, an image or a computer monitor must be 24-bit capable (8-bits for each color times three).
Each RGB color has 256 possibilities (8-bits define each one) so the maximum number of possible colors is 256 x 256 x 256 = 16,777,216 colors (in a 24-bit system). White equals R= 255, G = 255, B= 255 but in HTML code it is represented by the hexadecimal system which uses letters rather than numbers (white = #FFFFFF).