[mrerick]

Made this a sticky.

Some more background. This first link is for stainless steel:

https://bssa.org.uk/bssa_articles/he...heated-in-air/

These articles discusse "tempering" steel in general:

https://knifemaking.com/pages/forgin...at-color-chart

https://sheffieldgaugeplate.co.uk/bl...-colour-chart/

https://en.wikipedia.org/wiki/Tempering_(metallurgy)

And another article on tempering steel, in this case a lunch box:

https://www.instructables.com/Home-O...eringColoring/