I agree with Kasmira for the most part, but I think it's important to note what shade of brown the purse is. If it's a darker, almost black brown, there won't be enough contrast for it to look intentional--it would be like mistaking navy for black and wearing them together. However, a lighter brown could work, and I would prefer that over black, since a monotone outfit is rather dull.
If it's a darker brown, I'd just use black, though I strongly agree that a pop of color is always the best option. Combining neutrals is okay, but just okay. Adding colors, particularly unexpected combinations, makes an outfit a lot more exciting and less safe.
Can I ask why you're wearing an all black outfit at all though? If there's a way to incorporate color into the outfit itself--even if it's just a camisole--I think it will probably add some interest. Just curious.
