I have never had any trouble with bluing loss when using Bianchi, and Galco holsters, but I know some claim that the suede lining will hold dirt and ruin the finish. It may be true, but it hasn't been my experience. I suppose for every day use, it could start to eat into the finish, but for a hunt once or twice a year, plus other knockabout hikes, I doubt you will have any trouble with them.
The finish inside EPS holsters is pigskin, and is very durable, but soft, and it won't collect dirt, so it may actually be the best lining. I have a Tom Threepersons 1920 for my 4" N fames, but haven't carried a gun in it for any length of time yet, so I can't speak to that right now.