Created attachment 3012
Screenshot of the new display settings dialog
Add three sliders (red, green, blue) to the display settings dialog. The gamma correction is ajusted via the lib Xxf86vm.
Created attachment 3013
Patch against xfce4-settings-4.6.5
Thanks a lot for your patch. As Xfce 4.6 is the stable branch, such new features can't get into it.
As far as 4.8 is concerned, we are currently rewriting the display stuff using the xrandr API so this will have to be ported to this API in order to get into 4.8. I don't have much time atm but will eventually get to it, feel free to give it a try if you want to get it done faster.
While this is the older/original bugreport, the other one has a newer/more relevant patch.
*** This bug has been marked as a duplicate of bug 10069 ***