Created during the War of Fracture, Corrupted Dragons taint the lineage of all Dragons, metallic or chromatic.
The corruption taking root in different forms, some Corrupted Dragons were reduced to naught more than feral beasts, while others maintain their intelligence, albeit with a far more ruthless edge.
One should be able to easily perceive the difference between a regular dragon and a corrupted dragon, as their eyes become as black as a void and veins across the dragon bulge and glow an eery red, however, some Corrupted Dragons with their mental faculties intact may be clever enough to use magic to disguise this to unsuspecting mortals.