Right approach to change materials of actors by widget

I have a level with 6 objects, they are the same and I want to change colors. So I made a widget that appears on Left Grip when hovering a triggerbox near the objects. What I want is to select an actor and change color by the widget with the controller.

I am a bit stucked now how to set this properly up in an efficient and good way.
Have to say that I am quit new to unreal and learning everyday more…

Any help is welcome.
Thanks in advance!