The way I see it, you need to decide if you want to finish it like a British Fowler or an American Fowler? Most English guns were stocked in English Walnut which looks totally different from Black Walnut. The pictures I've seen of English Fowler's show a soft red color too them or almost no stain at all with the Marble of the English walnut coming through.
If you want a more American Fowler, then go with a deep brown almost black with a red hue to it. This can be accomplished by fuming the stock with ammonia, Ferris nitrate and heat, or commercial stains. However, go dark if this is the direction you choose.
Just my thoughts and experience.
M