Dragon

During the Dawn War , as the Gods and the Primordials battled, the gods Bahamut and Tiamat created creatures in their own image to serve them in their struggles. Over the course of these wars, the first dragons were exposed to many terrible energies. They became infected with the energies of the planes, corrupted by the powers of the Primordials, and imbued by the Primal Spirits with the powers of natural disasters. The creatures which are born in modern times tend to fall into two distinct categories. Chromatic Dragons are those that largely followed the tenets of Tiamat. Metallic Dragons are those that originally followed Bahamut’s teachings.
It should be noted that many dragons were dismayed by the creation of the Dragonborn race. Although they had been created by Tiamat, Bahamut embraced those who refused her paths as his own. Some metallic dragons chose to turn away from the Platinum Dragon’s teachings, just as some chromatic dragons, feeling betrayed by their mother, turned away from her as well. It is no longer possible to be sure of a dragon’s attitude by the coloration of its scales.
To add even more confusion, rumors persist of so-called "gem-stone" dragons being encountered that seem to follow the will of neither of the draconic gods and display mastery of Psionics. Time will tell if there is any truth to these tales.