Here is the thing:
I create a custom event in a actor blueprint call “change color” to change the color of box.
Here is my material and actor bp setting
Did you set your inputs? If you connect the B event to a ‘Print String’ does that actually print something? If not, set ‘Auto Receive Input’ in Class Defaults to ‘Player 0’.
However, as the other answer points out, that functionality doesn’t really belong in the level blueprint.