You should add a bar that moves all bars up or down in there current positions, so you can lighten things or darken them easily.
Or some checkboxes to lock bars together.
For example:
You check off red and blue, and when you move one of them the other moves
in proportion.
(If you have 128 0 64 and slide red 32 to the left, you should end up with 96 0 48, not 96 0 32.)
But, personally, I don't have much use for this.
I'm a total nerd and can pretty much nail the RGB code of any color shown to me.
Yay graphic design experience.