an RGB colour mixer

 xcolmix enables you to mix your own colours in order to determine three
 values (the R/G/B code, or red-green-blue mix) of a colour. You can use
 those colours to, e.g., define the foreground or background of X
 applications which support it. Furthermore, xcolmix lets you retrieve RGB
 values from the X system's database of `predefined' colours.