Bluing on only one pipe?

Hi Folks,
Just joined the forum as I used to ride a 2008 T100 Triumph but I recently picked up a 1980 KZ1000 LTD in very good condition with under 5K on the clock. It had been in a garage for 28 years so I took it to my garage and they switched the tires, lubed/replaced cables, spark plugs and cleaned the carbs ect. It runs pretty damn well now except the choke doesn't seem to do much and I have to warm her up by hand, which I don't really mind.
I just now noticed that one of the four headers are bluing, what does that mean on these bikes? My Triumph blued but they all seem to. Am I being too harsh on the old girl or are my carbs not as clean as I was lead to believe? Any other thoughts?

Cheers,
G

Most if not all of the Japanese bikes had double wall exhaust pipes from the factory,now if your pipes are aftermarket they might be single wall showing the exhaust temperature conditions. I'd pull the sparkplugs and see how they're burning.checked the compression?

Yeah I am pretty sure the pipes are stock, that is concerning. I will get the sparks out tonight and have a look at them.

Cheers
G

If you have a stock pipe turning blue you really need to find the problem because that cylinder is running way too hot. Ed

I'd suspect a cracked intake boot on that cylinder.