Usage:
rgb(Color, Red, Green, Blue)
Color is rgb(Red, Green, Blue)

Creates a color in Color by Red, Green and Blue. The variables Red, Green and Blue have to be between 0 and 255.

The Color is an integer and in hexadecimal looks in this way: 0xbbggrr, where

rr is hexadecimaly Red,
gg is hexadecimaly Green and
bb is hexadecimaly Blue.

If you use the predicate rgb then you can give it an integer for Color and will receive its components in Red, Green and Blue.
 

See also:
draw_point