RGB is a color standard containing Red, Green and Blue
The colorcodes for RGB can be generated in 2 ways. For mixing purposes they usualy use the 0-255 scale for each color. By example 255,0,0 would be Red and 0,0,255 would be Blue.
For viewing and online usage of RGB they usualy use the hexadecimal formatting. This type uses the 00-FF scale. By example #FF0000 means Red and #0000FF means Blue.