We recently upgraded to Microsoft Visual Studio 2012 at work and my first impression was that of staring at the sun... my eyes!  The default theme is a stark white-ish color, referred to as Light in the Options dialog.

Great, the UI is burned into my corneas, thanks M$!

If the searing whiteness of Light is too much to handle, you have one other option, Dark, which I find equally as jarring.

Who died my code black?  Or, is this the bastard child of Photoshop CS6 and Visual Studio 2010?
Luckily there is a quick fix, which has been around since Visual Studio 2010, simply navigate to the Tools > Extensions and Updates dialog, click on the Online section, and install the Visual Studio 2012 Color Theme Editor.

Make the hurting stop, Extensions & Updates!
This gives you a number of different options, I find the Blue theme to be soothing and serene like gazing into a digital meadow...aaaahh...

Cerulean blue is like a gentle breeze
Ok, I admit the Light and Blue themes aren't that different  but when you're glued to this UI for hours on end it's the little things that matter :-)