The RGB Color-Naming System
The RGB color system is commonly used in both web graphics and web documents. This system is was designed to define colors as the human eye perceives them, as light. The three foundation or primary colors of this system are red, green, and blue.
The color system is additive: varying values for red, green, and blue can be combined to form the other colors. Because the system is based upon the properties of light, an absence of all color is black and full saturation in all colors is white. Each secondary color is the sum of two primary colors:
Red + Blue =
Purple
Red + Green = Yellow
Green + Blue = Cyan
RED - GREEN - BLUE
This system allows for the creation of over 16 million different colors. All 256 grayscale colors are included in this color system.
Listing the RGB Colors. Because the RGB system defines over 16 million colors (256x256x256=16777216), it would take many pages to display them all. It is also difficult to distinguish colors that have very similar values.
A good reference for a broad range of colors are the 216 colors commonly used on the web. These 216 colors form what is known as the "web-safe" or "non-dithering" color palette. They were traditionally used to prevent color-mapping or dithering of images when the majority of computer displays only supported 256 colors. Although most displays today are capable of representing millions of colors, this palette still remains popular.
The only digits used in web-safe colors are 0, 3, 6, 9, C, and F. As you can see in the chart, the convention is for the values of red, green, and blue to use the same value for both digits.
There are C Y M K Color system, which is secondary color from RGB for specialized graphic system and for printing.