Three Doors

--SPOILER--
.
.
.
The door with the faintest underside "shadow" coloring is always the correct door.

Like YLed said, room 85 is where I had trouble opening doors; only the correct door would open for me. Then at room 89, none of the doors would open, even when I went back to use up any remaining keys, even the last key.

Doors are bugged around room 88/89. Had lots of keys and couldnt open any