I wear my berets with EVERYTHING and they always look great. I have a couple of black ones like you see anywhere and used to have a beautiful purple one that I got from an army/namy type store in Florence (once while wearing it, I was very "politely" informed that only the most elite of special forces in the Israeli military could wear that colour) and an actual UN "Peacekeeper" blue beret from a friend in the Canadian forces.

One of my favorite hats, actually. I've also been known to wear my porkpie with my kilt as well (kinda like a fedora, but with a shorter crown and a smaller brim).