If it can't be removed is there a way to reduce it?
After 38 years, the pipes on my KZ305 were perfect. Then I got my hands on the bike and blued them in a month. The bike was way to rich and fouling plugs when I got it. My first attempt to fix it, got it too lean and blued the pipes.
I also have a CB650 with blued header pipes.
There isn't much that can be done about exhaust blueing without causing some damage to the chrome.
Then again, someone will probably chime in about a miracle product. hee.
Chrome polish usually contains some sort of acid &/or abrasives. I tried Blue Job, Mothers, Semi-Chrome, Turtle wax chrome polish & Blue Magic but nothing would remove the blueing. I was able to remove some of the browning on the mufflers, but that's about it. I tried using bronze wool aggressively w polish but that left a dull spot.
I have to agree with Martin on this one. Once blued pipes take place it's a no-win situation. The best I ever found was Semi-Chrome polish but it is a bear to work with. It always seemed like once the pipes blued they were more prone to bluing if you cleaned off the old blue color. A lot depends on how blue the pipes really get before you try to correct it. The longer you let it go the more difficult to remove it.
According to some of the posts in the link below, the real culprit are the sulphur-bearing brighteners typically used in the nickel plate that is under the chrome. If true, the only real solution is to completely replate without the brighteners.
Step 1. Find out why the pipes suffered excessive heat and turned blue.
Step 2. Correct that problem.
Step 3. Replate or replace the pipes.
Chrome plating is extremely thin! Decorative plating, such as exhaust pipes, is usually 0.000005" - 0.00001" thick. That is really a thin plating, so trying to polish its surface doesn't work particularly well. If the pipes on your bike were the originals they were dual wall. The inner pipe gets crazy hot while the outer pipe still gets hot enough to melt your skin but it should not turn blue unless something is wrong and the engine is running too hot. So before replating or replacing your pipes nail down the reason for the excessive heat or you will quickly damage the new pipes.
Here's a picture of the bottom end of a stock KZ650 exhaust pipe. Notice it is a pipe inside a pipe. Ed