Thank you!

Thank you about the cropping. The "grunge effect" was accidental. It didn't show up until after I exported the png to my hard drive and had already closed it in GIMP and discarded the changes. The effect is from oversharpening in an image that has way too much daylight in one corner and way too much darkness in the other. Hope that helps you if you wanted to accomplish the same!

No problem! Start with the color levels, then the color curves working only with lights and shadows. That's what makes a huge difference in your light levels.

Took me awhile to learn the sweet spot; everyone was always telling me my icons were too dark. lol