Graphic Doesn't Hide Behind layer

I have been working on my animation and recently discovered that when I change my background color, all of my colors change depending on the background shade. The main issue is when I have a door that opens up and dissapears above the wall.. When the door opens,  it is seen through the wall even though it is supposed to be hidden under that layer. It is not fully seen as it becomes slightly transparent depending on the amount of layers above it. Is there anything that I can do which can fix my problem?