Red plates don't seem to do anything
You just got to move over the red plate once to activate it. If you don't, the door wont open even if you have cubes on both the white plates.
I didn't even touch one of the red plates and the door still opened.
Ohh.. I didn't see that before. I'm sorry for the inconvenience, I'll patch it up when I can. Thanks for pointing it out.
