Need help with shape identification

Hi, so we have this simple project to do: We have a few different black forms we film in front of a bright background. We want the background to take on a specific color and a specific music to play in the background to every form.

My idea would be to change the whole scene somehow to black and white, 0 or 1, then somehow identify the shape and with the data play the specific music and somehow make everything that is indicated as 1, white, in the picture to take on a color, say red.

My problem is, I don't know the objects to do this. The black and white part is surely the easiest. But can you tell me an object to identify a shape on the screen? And more importently, there has to be a way to color the background, but I have no idea how to do it.
I really would appreciate any help I can get.

Thank you!