are you changing the mirror you have now, or leaving as is?

if the mirror stays-I wouldn't frame it since it touches the backsplash...frame usually implies some distance betwen one surface and the other

I know people do it sometimes but it doesn't look good, proportion wise

you can try and raise your mirror but I doubt you have enough space for that..you probably have vanity light there

if the mirror goes-many possibilities. Don't see black, brown or gold but do see white, silver, something like bone inlay (say, warm gray plus pearl white..but I'm saying warm gray purely relying on your current accessories, otherwise I'd look at another combo)..can be something pretty with beveled edge, etc, so the frame of the mirror is actually a mirror too.

I'd decide on the overall plan, then narrow down to size/shape/orientation..then to a particular frame.

another idea though-the mirror stays..and you attach a frame you like inside it, bringing more interest. I'd say harder to pull out though. But one can get interesting result.

The same white that the vanity is

We framed ours and it touched the backsplash. I loved it and thought it felt more finished. Taking out the backsplash wasn’t an option so we made it work. I would paint it white. I think white gives a bathroom a clean look.