A television works by internal beams of light hitting hundreds of receptors on the inside of the television screen and causing them to light up. Each receptor inside the screen makes a small dot of light and color that combines with others to form an image your brain can interpret.
The function of television is predicated on two functions of the human brain. The first is that the brain can create a functional image out of collections of small dots gathered together. The second is that images presented in quick succession appear to be moving to the human brain.
A television uses these two principles to create images and motion. A light inside the television screen rapidly moves across the screen in thin lines that produce the image. There is only one light in black and white televisions. That light turns on for every receptor that should be white and turns off for every receptor that should be black.
Color televisions have red, blue and green lights that fire at receptors in the appropriate colors. White is created by lighting all receptors and black is created by turning off the light entirely. All other colors are combinations of red, blue and green. Color television signals have an extra frequency that black and white televisions cannot interpret. This means that color television signals are interpreted as black and white images on black and white televisions.