Courtesy of Rhett Allain
But what about color from a video projector? It basically does the same thing. However, instead of a series of small RGB lights, it projects RGB colors to different locations on the screen.
Black mat
Now we're ready for the fun stuff. How do video projectors emit black light? Black light would be the absence of any bright, as we saw before. How come you don't project anything? First, think of the screen like a TV. If you have three small lights (red, green, blue), you can create a small black dot by turning off the lights for all three colors in that location. Boom, it's black!
So is it possible to just turn off the projector to create black? That can't be right, right? If that's the case, you won't be able to tell the difference between projected black and a screen that doesn't turn on the projector. Yes, that's exactly how it works.
Take a look: In the following image, I'm showing a slide that's half black and half white. The slide takes up most of the screen.