jetting question

I've just recently ordered, but not received a Twin Air Filter, and FMF Jet Kit. I plan on adding an FMF Powerline exhaust but that will have to wait a bit. On to the question.

I changed my spark plug the other day and noticed when I pulled the plug it was showing blue/black deposits. From what I've read this is a sign of it running rich? If after adding the exhaust, is it always necessary to rejet? I know just changing the spark plug has made it idle a heck of alot smoother.

I guess what my thoughts were, is if indeed it is running rich that by getting better air flow, it would put it potentially where it needs to be.