The three black and white transparencies are different from each other. Each transparency was produced by photographing a full color photograph with black and white film and with a colored filter in front of the camera lens. All colors visible to the human eye can be apporximated by mixed three primary colors.
White light is made up af all colors.
When we properly balance a mixture of red, green, and blue light, we see white light, color vision therefore is an additive process. When you block out one colored light with your hand or with the paddle, you subtract it from the total . We'll be adding interesting info and links here.