RGB
RGB stands for red, green, blue. In an uncompressed true-color image, each pixel of the image is defined by three bytes that define how much red, green, and blue light are added together to produce the color in that pixel. Textures can also have a fourth channel, called alpha, that can store other information for each pixel (usually opacity).
- The three or four separate values for each color are called "channels." Shaders in Source can manipulate each channel individually to produce color effects.
- Within materials, an RGB color is a material vector.
Note:Sometimes the red and blue bits are flipped, which is called BGR. BGR encoding is intrinsic to some formats, such as TGA or 
DXTn, and is the preferred format for SDR textures in DirectX 9 and earlier (newer versions of DirectX prefer RGB).