In painting, which is a form of subtractive color, red and yellow together make orange. In additive color, which is used in television screens, orange is formed from one part green to two parts red.
When surfaces reflect light, they often only reflect certain parts of the spectrum back to the eye (the others are absorbed). Therefore, subtractive colors work by taking away or letting the object absorb certain parts of the spectrum to form a color. Adding more colors in this type of system moves the color toward black.
Additive color, on the other hand, works by projecting light. By mixing different colored lights, new colors are formed. Adding colors in this system moves the color toward white.