Unity UI Toggle Button: different color for ON and OFF state?

Hey guys,
trying on this for hours now. Can you tell me if there is an build in way to set a ToggleButton's color depending on it's state (on/off)? More in detail: I have a toggle group, where only one toggle can be in the on state at the time. This should be visualized by the toggle color. All off toggles white, the on toggle gray. Seems to me like the most normal thing, but I don't get it working.

Of course I could write a script doing this, but it feels so simple that there is maybe a build in way.

Thanks, Tobi

 

Seriously this should be simple. How do we do this?