Fiebing's used to call their Pro Dye "oiled based", but later changed it to just Pro Dye to reflect the fact that it is not in fact oil. I asked the same question a while back.
The Pro Dye is reputed to sink deeper into the leather than the regular dye, hence costing more. It is what I use.
It will dry and stiffen the leather a bit. That is why you add neatsfoot oil to the leather to bring back the softness lost in dye work and tanning.
I have had dyed leather (with no neatsfoot added) to split open and crack when flexed. The time to "break" the leather is before dye.
Chocolate brown is indeed dark. Thin it, and you can creep up on the darkness you want in layers. Another trick is to use a lighter color dye, and keep adding coats to make darker browns. I have noticed that it is best to let a dye coat sit overnight to let the dye penetrate and dissipate into the leather surface. It will be lighter when you return to it in the morning. Rub (burnish) with a cloth as hard as you can between coats to get any fugitive dye lurking on the surface.
The "Show Brown" makes a very credible vinegaroon color. It does not add the vinegar acid to the leather, which is a very good thing long-term for hide and stitching.
These are all just my opinion and what I have learned thus far on this road. I may learn better ways of doing it later on. You may find something better that works for you.
God Bless, and best wishes, Marc
