Lined and hardened, as though by exposure and want of personal care, there was also a lack of sensibility, an almost animal callousness, on the coldly lit eyes and unflinching mouth, which readily suggested some terrible and recent experience--something potent enough to have dried up the human nature out of the man and left him soulless.
Eye colors depend on the amount of pigment (melanin) found in the iris and how it is distributed. Light gray-blue eyes contain much less pigment than extremely dark brown eyes. And there are many shades of eye color in between.
Unfortunately, there is no eye color that has been fully agreed upon as the rarest, though green-eyed and amber-eyed people are both extremely rare. In fact, the rarest eye color is different in different geographical locations. In some parts of the world, green eyes are rarer than amber eyes or vice versa.