The reason is you are probably thinking you want red, use red ink? Blue? Use blue ink? Well, that works if you only want to print those two colors but think of all the colors in a photograph. To create all of those colors you can’t use thousands of colors of ink instead you need to mix different basic colors to get them.
Now we have to understand the difference between additive and subtraction color.
Additive color starts with black, no light, and adds colored light to create other colors. This is what happens on things that light up, like you computer or TV screen. Go get a magnifying glass and look at your TV. You will see little blocks of red, blue and green light. All off = black. All on = White. Varying amounts of each = all the basic colors of the rainbow. This is called additive color.
Now with a piece of paper, why is it white? It because the light is white and the paper reflects 100% of it. A black piece of paper is black because it absorbs all the colors of that white light and none of it reflects back to your eyes.
