The brown spot on the muffler is normal, it is where the internal baffle is located. I've had two different sporty mufflers on my '02 so far and both have developed a brownish/blue area part way down the length. I'm running a 152.5 main jet which is a little lean for my setup so the blueing was expected on my ride. I like the effect, makes the bike look like it has been ridden, not polished. Follow the rejet advice to get your's running a little more on the rich side.

LOL