I've always been a fan of mixing navy + black and love that it is popping up more and more. I usually lean towards more of a bluish navy instead of a darker shade that might look more black. I think that is the is key when mixing the two colors, you want to be able to see the contrast and not have people thinking "did she think that was black?" or "did she think that was blue?" Which is why the knotted panel dress from Zara is the perfect shade of navy. And how fun is the detailing in the back!