$rgb
From Scriptwiki
Note: This identifier works in two ways, both explained below.
Style 1
Returns RGB value of specified system color name which can be one of the following: face, shadow, hilight, 3dlight, frame, and text.
$rgb(name)
Style 2
Returns an RGB color value for use in /draw commands. If you use only one parameter, it assumes it is an actual RGB color value and returns N,N,N.
$rgb(N,N,N)
Example
$rgb(face) ;returns RGB value of face system color
$rgb(80,10,10) ;returns 658000
$rgb(658000) ;returns 80,10,10