It is as simple as the title makes it. The walls are blue and the floor and roof are green. No need to download the textures or models because the content is packed into the bsp file (thanks to a handy tool called VIDE, or Valve Integrated Development Environment) and there are no models. The lighting is just one light entity set to the value "constant" and the textures are unlit so they shouldn't be effected by lighting, but models may be. I made this map by hand, and sorry, there is no way to make the walls green and the floor and roof blue. I will add a mp4 file of how to use greenscreens/bluescreens.