STAINLESS STEEL DISCOLORATION S082
When stainless steel gets hot it turns color.
If there is a question as to whether the color is on, or in the metal, try to erase it with a common pencil eraser. If the color comes off it means the piece did not get hot, something was stuck on the stainless steel.
The following chart will help you to determine the maximum temperature the stainless piece may have been exposed to.