Ronald, All stock single wall pipes will blue some time or another. A big cause of Bluing is a badly tuned bike, burning rich or lean putting more heat into pipe.
There are polishes available to remove the Bluing, and some people on forums, they suggest to remove and with high heat paint, put several coats inside of chrome pipes.
Check the attached links,instruction and guides, Good luck
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Exhaust Bluing Twin Forum Harley Davidson Forums
Exhaust Care
How to Fix Bluing on Motorcycle Exhausts DoItYourself com
