Never Dull
Eagle One Never Dull (in the little silver cans) will buff those annoying brown spots out, unless they are actually chips in the ceramic from rocks thrown by the front wheels. It will still get the brown discoloration off, though, even if it can't fix the chip.
For brown showing up on the weld seams where the mufflers are welded into the sidepipes, you can use Mother's Mag & Aluminum Polish and a toothbrush.
Both of these can also be used to soften road tar spots on the pipes to the point that you can then scrape the tar off with your fingernail. Never Dull will also removed melted-on nylon from your sidepipes, but it takes a little more patience to buff something like that off.
Hope this helps.
Zach Butterworth
289 FIA #9367