You already have three very neutral colors: Noir, Etain, and Gold, so I'd definitely echo what some have said here and go with more of a "pop-of-color neutral" with your next one. Rouge-H or some type of dark/navy blue would give you some added dimension to your wardrobe. Surprisingly, I find Rouge-H very neutral and easy-to-pair with different outfits, while adding that bit of dimension to your look...don't hesitate to ask your SA to at least look at a bag in one of these colors to get a feel for it before you settle on what color to ask for in your B25.
Thanks for your advice. You made a point, I haven't thought of it. I will ask my SA to look at a bag in the colors!