What causes the bar to turn blue-black like that... Heat from a dull chain? Oil issues... too tight?
I was over at my brother in-law's place a few weeks ago and we cut up some winter fallen oak and maple. My Husqvarna 450 was out cutting his 16" Stihl. I don't mean that as a saw comparison, just an observation. His bar had those same black-blue marks on both the top and bottom. I noticed he cuts using mostly the far end of the bar. That's where the the marks are.
I tend to rock the saw through the log with the dogs on the log. My saw is only 3 years old but it's bucked several cords of logs and almost all the paint is still on my bar, while the BIL's bar has almost no paint left on it and has big blue-black burnt looking sections. Is he running the saw too long on a dull chain?
I should have checked out his chains for sharpness and tightness