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.
You can candle the eggs after only 24 hours of incubation and begin to see the first signs of a fertile egg. I usually give the egg a full 4 days of incubations before I decide to pull the infertile ones.