I have signed up just to reply to your question .
The yellow color you see is the temper color of the steel.
It is used after quenching(hardening) to temper the hardness of the blade to soften it a bit up , a knife that is too hard doesent mean it is tough , apply a bit of force to it and it will snap in 2 or a million pieces, you make the blade tougher by slowly heating up and watching the "temper colors" of the steel and depending on what you are making you want a different temper on different steels and tools you make , so for example if you make a knife you want to get to that yellow or what we call straw color , for an axe you want to soften it a bit further to maybe purple color.
The yellow stain can be removed with scratching(sandpaper) as this color is formed only on the surface layer you can also try using vinegar and baking soda or maybe even just with vinegar , it is rather quick...I learned this the hard way. I have made a knife and I wanted to keep the temper colors on the spine of the knife , it was a little rusty when I left it for a few days so I placed it in vinegar to remove it , this removed the temper colors as well..
Good luck I might be too late for this post. XD
Oh by the way no need for special products just use plain old white vinegar and baking soda.
Forging temperature of steel is much higher yes but tempering of steel is done at the range of 250-350 °celsius
Which keeping a pot on a stove can definitely achieve .. I've used an oven to temper my blades it works flawlessly.