Carbon or stainless damascus? and what are you doing this too, a knife perhaps? What will this be used for? The whole process might wreck the tempering in the metal and it will be unsuitable for use as a tool.
Its hard to say without knowing the types of steel and possibly other metals that compose your damascus. Different steels have different tempering processes, most of which involve controlled heating or cooling for very specific lengths of time.. The issue with damascus is that it is a mixture of steels layered and forged together and then it is tempered.
I am not sure how the tempering process of damascus usually goes. Some steels are baked at 400 degrees for a couple of hours. Some are heated and quenched in oil, some are thrown in baths of liquid nitrogen.
And heating it for color case hardening will probably affect the temper.
Are you thinking about doing this to carbon or stainless damascus?
If you are working with carbon damascus, it is possible to add a patina to carbon steel by applying mustard and water to it.
Here is an explanation of the process of forcing a patina to carbon steel.
Look into acid etching, I think it is the last step that is usually used on damascus knives to provide more contrast to the layers. Its a cold process that only effects the exterior of the knife whereas case hardening is a hot process.