What means the color-coding on the button master / multi in Ableton Live?

On my KeyLab MK II I realized that the right most button (below the slider, labeled ‘master / multi’ changes colors from green to soft green to blue to white.
But I have no idea what it controls or what effect that button has.

Any ideas, what this button does?

I found out myself:
The button toggles the destination of the knob above the slider from pan to send A to sedn B.