Obstacles

Doors
There are 3 types of obstacles. Doors, walls, and restart spots. Doors can be activated by having a player click on the pad (thats the same color) the required number of times or have the required number of players on a sensor (the pad that players have to stand on to deactivate). If a player is in the way of a doors space when it closes, the player will teleport to the nearest open space or door. If a player is drawing and a door is on the right or bottom sides, the drawer can't fill in those spaces (this applies to walls too).

Walls
Walls however, can't be deactivated by a pad or sensor of any kind. Walls are black and players can't go through them. Every level has a wall in it except for level 1 (and the starting screen). Walls are the most common type of obstacle. A wall most likely is to surround a green door with a door blocking the only entrance.

Red Areas
Red Areas are pink/light red and if the tip of your cursor touches it, you restart the level. So far, only 3 of the levels have red areas.