They have one or two formal nights per week and you can either go black tie or lounge suit and tie. The Mediterranea is a super ship and I am sure you will have a great time - definitely try the Club Medusa for one evening meal and if you stick to their set menu it costs a surcharge of about £20 per person but if you like superb food and service it is superb and formal attire is not needed only being smartly dressed.
Dress Code On formal evenings, women wear everything from party dresses to glittery gala gowns. Men generally opt for dark suits rather than tuxedos, though Costa has a convenient tux rental package. There are two formal nights on a seven-night cruise. Other nights in the Caribbean are casual, the ultimate in casual being the last night's Roman Bacchanal when the crew hands out bed sheets to be worn as togas. I was surprised to see that only half the passengers participated. A number of past Costa passengers went all out, bringing their toga gear from home.