smetzger said:Could you see the Black Pudding if you had a light source? After all its the same color as the rest of the room.
Yes, however color is not the end-all be-all of vision. Texture also counts.
Plus, you might want to read the physical description of the monster. Your average black pudding is two feet thick! Even if it's the same color as the walls, it's certainly not the same shape as the wall or floor is supposed to be. It is a huge (literally, in game terms) lump. Kind of hard to miss that sitting in the middle of the room.