This is additive color. Red, green and blue are the primary colors of white light. All three colors will result in white, the absence of all three will produce black. When two primary colors of light are added together, you get a color that is brighter than either of its components.
MYTH: A blood spot inside the egg means the egg is fertile. FACT: A blood spot inside an egg can occur at various points in a hen's reproductive system as a result of a blood vessel rupturing. It can be the result of a genetic predisposition, a vitamin A deficiency, or a random event.
Start candling your incubating eggs at day 4 of incubation. In fertile eggs you will see a small spot (the embryo) with a web of blood vessels radiating out from it. Conversely, infertile eggs will either be clear, or show a dark ring. This video shows a viable chicken egg at day 12 of incubation.