Is the maker Caspian Arms? If so it looks like it is a mix of 2 types of stainless steel.
what you are looking for is acid etching. managed to find this discussion of a Caspian Arms damascus 1911 slide.
the slides caspian sells are two variations of stainless steel. as you work on them they do not show the variations - they just look like a stainless part. you must use an acid bath to bring out the damascus pattern. the acid etches the different steels at a different rate. a quick bath produces less effect than a longer bath. more polishing of the part will highlight the effect as well, slightly though. the biggest difference is the amount of time it spends in the acid bath.
General process of this is easily findable with a google search of "stainless damascus etching" most of the results will be about knives but that is ok because it is the same process.