Why you get dark circles when you don't sleep?

Question

I want to know the scientific cause of the color black and the relation with the lack of sleep, I don't want a solution for this problem.

Answer 1

"...Another cause of undereye circles is eyelid swelling during sleep. When you lie down, gravity can cause fluid to collect in your lower eyelids. This swelling may create the appearance of shadows below your eyes..."

http://www.mayoclinic.com/health/dark-ci...

"... dark under-eye circles are not your fault. They don't mysteriously appear when you misbehave or are stressed out, only to vanish when you get 8 straight hours of sleep. Dark under-eye circles are a by-product of the very same mechanism that produces bruises (and you don't blame yourself for bruising, do you?). Changing your behavior will, in almost every case, NOT get rid of your dark under-eye circles.

Having said that, onto the specifics:

What causes dark under-eye circles

Your shiners, your raccoon eyes, your blue luggage... whatever you call your dark under-eye circles, here's what they really are: oxidizing hemoglobin.

Dark under-eye circles begin in the capillaries, the tiny blood vessels that web the delicate skin around the eyes. Now, your capillaries are so small that red blood cells sometimes have to line up, single file, to get through. Frequently, red blood cells get lost and wander into the surrounding skin. This isn't a problem - it happens all the time - and your body has a mechanism to mop up these escapees. Enzymes in your body break down the red blood cells, including their hemoglobin (the molecule that gives them their distinctive red color).

No problem, right? Except for one thing: when hemoglobin is broken down, its remaining components have a dark blue-black color. Just like a bruise. So your dark under-eye circles are actually caused by leaky capillaries..."

http://www.darkcircles.net/under-eye.htm...

Answer 2

My understanding is that the discoloration is a result of blood leaking from the capillary beds underneath the eyes.  Essentially, you are bruising when this happens.

To answer the question, "Why does this happen when you don't sleep?"...I'm thinking about it, and not sure why.  Guess I can't answer that part.