Blender interface appears gray? I'm not sure what's going on, but today in the morning when I opened blender it had turned gray from black. 

I don't think it's affecting any type of performance, but it is not feeling right while working, is there anything I can do to revert this change?

I'm using Blender 2.50
Blender is gray by default:



So it sounds like the theme you were using was somehow reverted.

There is a black theme bundled with blender called Back to Black. If you select it in File menu > User preferences (or CtrlAltU) > Themes > Presets, then blender looks like this:



To set this as your default theme, click Saver user settings at the bottom of the user preferences: