Can you set a camera to not render a certain color? As in, wherever it sees that color, you see the clear flag, (whether that be depth or skybox or whatever). Kind of like applying a chroma key to the camera.
The camera isn’t responsible for putting the pixels on the screen. It just determines what objects need to be rendered and from what direction they are seen. How a certain object appears on screen depends on the shader on that object. In the fragment shader you could exclude a certain color, however when using lighting / shading of any kind it’s almost impossible to key a certain color. If you render objects with some sort of self-illum shader that should be no problem.