The formals nights range from tuxedos and formal gowns to jackets and dress shirts and ties and pant suits. The last 2 week cruise we were on only had 2 formal nights, but that was on Princess. The Caribbean is no less formal than any other venue. Have a wonderful cruise!!
It seems to be quite OK to dress up on any night aboard a cruiseship! One of the benefits of a cruise is it is fine to get all decked at dinnertime-and you won't be alone!