Look at the arrow that is on the projector. Now look through the lens and onto the focusing board. The image of the arrow is flipped because the lens is curved. Each switch controls a different tube of gas. When you turn the switch on, you excite the atoms of gas and they produce light.
Different gasses produce different colors when excited.
Try looking at the lights with the glasses. These are diffraction glasses. They split light up into the different colors of the rainbow. Swing the tube as fast as you can. Cartoons and movies are made the same way.