|Spoiler warning: Plot or ending details follow.|
Go to the blue door and find a small room with a moving wheel. Interact with it to recieve the effect.
Go to the door with bloodstains on it and find a bleeding thing with a pitchfork in it. Interact with the right side of it to recieve the effect.
Go to the door with bloodstains on it and interact with the green trashcan. The trashcan should take you to a colorful area with pink grass.
Go right and interact wih the second monochrome door. Once you're inside, interact with the chalkboard to recieve the effect.
Go to the blue door and interact with a monochrome door. You'll be inside a blue maze. Find the rectangular NPC and you'll be in a desert with gas tanks.
Interact with the tank with a bloody window. You'll then be in a black map with more gas tanks. Find a tank with a mouth for a window to recieve the effect.
Once you find all of the effects, interact with your door in the real world to view the ending.