I would/wood say your ok in what I have experienced over the years, I have bent a lot of Osage without color change...You don't need to see a certain color or burn indication such as charred...When I use steam it stays where I put it without color change other than maybe a water stain...It's all about temperature...The finish of a piece of wood, such as a glassy fine finish vs a rough 60 grit will change using a heat gun because of all the small fibers that have raised above the surface, they will char quickly...I want my bows to harden deep into the belly beyond a charred surface on the belly...My opinion is, the charred most outter surface is weak in compression similar to charcoal...Color change can and will happen but I don't use color to depict temper....
Don