Cover Up for Light Oxidation?

No fix that Iv'e found . Black face can be even worse .

http://www.ehow.com/how_4516531_clean-anodized-aluminum.html
Several ways to clean oxidation off anaodized aluminum. (which is what you face panel is)
I would take OFF the faceplate, and do the cleaning carefully acrosss the entire face. So if it changes the appearance a bit, it will be evenly colored.
If you try to just do a tiny bit, it will probably still look different. And trying to do the cleaning around the knobs etc, will also leave a pattern in the finish.

Thank you, both. I've uploaded a picture to my System named Oxidized Faceplate, so you can see it. When you're looking head-on it's barely visible, but with a side view it's easy to see.

Be careful with strong chemicals , Aluminum has a type of plastic coating , once its removed the alloy will discolor and attract dirt at an alarming rate .