Automatically change the Materials. About the Blue Print.

I have a question about automatically changing the Materials.

There’s a box in a certain area, and this box…
The two colors of the Materials are automatically changed.
Once the player enters, one of the two colors will be used for the muster.
It’s changing, and when the player leaves, two more mutials…
I want to make BP that is automatically changing.

I would appreciate your help in this regard.

Master? Monster? Materials?

No clue what’s happening here. What is changing the colour of what and when?