Heh,
Dragons of different colors are akin to us having different "skin colors", ie different race. But in the AD&D fantasy settings. Different color dragons also hv different abilities. Eg. Gold dragon are the most "powerful" and intelligent dragons. Blue dragons hv lightning as their breathe weapon versus red dragons hv fire as breathe. So there's white, green, blue, red, silver, gold, copper, bronze, black, shadow (any i missed out?)
Gold, Silver, Copper & Bronze dragons are the "good" guys.
Red, Blue, White, Green, Black are the "bad" guys.
Shadow dragons are unnatural creatures
As many role-players love dragons, there're tons of development around dragons - down to the minor characteristics of each type of dragons, eg. Gold & Silver dragons like to appear as human form. And there's even a completely different set of creatures borne unnaturally out of dragons in a particular era (called draconians). TONS of interesting things around dragons....