Look at the TV screen through a magnifying glass. You will see a grid of red, blue and green dots. All the rich colors on the screen "draw" these three colors. For example, if you want to portray a red spot, lit only by red dots. And if you want to get some kind of color (yellow, pink, purple, and so on), to join the dots of other colors, only they glow all with different brightness.
If you look through a magnifying glass on a white area of the image, you will see the same red, blue and green dots, glow equally bright light. This means that white light is obtained by the sum of the other colors.
With an illuminated screen is clear, but how does the color non-luminous objects? If such items to illuminate white light (consisting, as we have seen from experience with the TV, from the colored rays), then some part of colored light absorbed by the subject, and some will be reflected. And depending on the "set" reflected rays we will see the color of the subject. Black body absorbs all the light and do not reflect the white - on the contrary, reflect almost all the light. That is why dark objects heated by the sun is much stronger than light.
But what if to cover, for example, red light blue object? A blue object reflects only blue rays, and if we covered his "real" red light, in which there is no mixture of blue light, then from our subject, nothing will be recorded, and it will seem black.