I've done several floral style western holsters in the from the Will Grohmley barbecue holster pattern pack. They have a Glock pattern in there. The holster has great coverage and there's plenty of room to do tooling. The only reason I would go with a brown color is if I was going to do tooling and that's just to show off the tooling itself. Otherwise black is the way to go. However if you do want to do brown on a veg tan leather my recommendation is to get olive oil. Continue to go over the leather with olive oil until you get the color brown that you want. You can even add an antique paste that will highlight the raised spots on the holster. As far as edge coat I would go with a dark brown. There are benefits to the olive oil in that archaeologist are still finding pliable leather from the Roman period that was treated with olive oil. The picture below is of course not of a Glock holster but it is a holster for a Colt Python. I dyed it with olive oil and then used the antique paste.