Some people with blue eyes get headaches if they’re out in the sun too long; the lighter the blue the worse the headaches. Ligher eyes let in more light, and are more sensitive to sunlight. People in the northern countries like Sweden, Norway, Denmark, Finland, etc often have blue eyes (along with blond hair, which often, but not always, goes with that trait) because the sun is less intense up there so they don’t need dark eyes to block out more light, like they do in Africa and the Middle East, where most people have dark eyes.
As for the Middle East, the blue eyes usually appear occasionally in non-Arabs, i.e. Turks, Iranians, Pakistanis, and Afghanis (also green eyes for the Afghanis). They rarely show up among the Arabs; the only blue-eyed Arab I can think of is Bashar Assad (and a mutant he is!)
“Lighter eyes let in more light, and are more sensitive to sunlight.”
This blog entry from the Gene Expression website talks about this and theorizes that this different amount of light changes the actual personality of blue-eyed people.
http://www.gnxp.com/blog/2007/11/blue-eyed-ice-queens-and-brown-eyed.php
It also claims more men are blue-eyed and more women are green eyed. Also, the less emotional and more analytical blue-eyed men are more often found in professions that correspond with those traits such as engineers. There’s an exception for East Asians with a plausible reason given. It’s a very interesting theory (and I’d never heard of anything like it before) but more recent studies need to be done.