The chart is for raw (unpainted) mild steel. I see some of those colors when I cook raw steel in the oven to make sure all the oils are off.
I guess the point I was trying to make was "be safe" above all else
I powdered a few of our slide in racks for our oven. After a few weeks the racks were a little singed and discolored, we normally run at 400F.
Galvanized steel and higher temperatures don't mix.. totally agree about the elbows
Have a great weekend