Final boil and stack issue

[Lazarus]

This year we got a brand new oil-fired 2x6, all stainless case, all stainless pipe. I am literally in my last hour of boiling for the season. Have timer set for every 5 minutes. I add defoamer, check the pans, verify the stack temp. Rock solid 700 degrees every time. Significant other walks in, looks at the stack, and says what happened? I look and the stack is yellow from the base up past the damper. What?! Definitely not like that 5 minutes ago. It was perfectly consistent all night at 700 degrees, still at 700.

Is this normal, or did I just ruin my pretty stainless stack? I've been boiling all season with no issue.

Or does everyone's new oil burner stack look like this?

[backyard sugaring]

Do you have a flue damper on it? Lee

[Lazarus]

I do. Here's a picture.
9303

[jmayerl]

That is the standard copper color that SS turns after having high heat applied to it. I could show you many pics of transition bases like that.

[Super Sapper]

Mine turned a purple color last year.

[maple flats]

That's not ruined, just seasoned. It will be good for many years to come.

[village idiot]

Straw color. All it means is the stainless has seen some heat. Use it as a point of pride cause it means you have your arch firing down pat.