Well, I guess that's a good point. From what I could tell from the picture I thought it was a pre-dyed, vegetable tanned leather. I can see that the edges are dyed black. If it is a dye job after the fact (tanning) then it can be some other things. If it is oil-dyed then you wouldn't really have an issue with color change after wetting. I don't know if you had this made from someone or it was an already built rig when ya bought it. If ya know the maker ask him about what kind of leather he made it out of and if he dyed it himself, and if so, what type of dye did he use.
I have molded pre-made holsters for guys with a guess on what it was dyed with before. I have gotten lucky and did not have any color runs!
In my earlier days I wet a project down that I had already dyed and ran color everywhere
kinda where I started using oil dyes.