Which cruise line are you going with? I would check on their website or in the brochure becaue they often stipulate how formal you are expected to dress on an evening (DH used to work for a 5 star cruise line, they provided pretty much an itemised list of what to pack for each day/evening! I got away with slobbing around below deck though ) I would go for a mixture of dresses/long skirts with nice tops but take a good mix of pashminas/light cardigans as it will be chilly on deck in the evening.
I went on the QM2 in 2007 and took casual clothes for daytime, trousers and tops etc. A couple of people were wearing jeans and there were lots of shorts but mostly it was smartish casual. Not sure what the weather will be like where you're going, am assuming hot but it gets very cold on deck when you are at sea so something warm would be useful. They were a bit funny about what you wore in the restaurants during the day, no bikinis or hairy topless blokes!
Evenings were very smart with a couple of formal evenings so black tie. However if you didn't want to get tarted up you could go to the less posh eateries in normal clothes.
Totally didn't read your op . Yes anything from posh frocks to smart trousers and tops with a smidge of glitter on (!), long skirts and tops. Black dead easy if you can't be arsed but you'd stand out beautifully in a splash of colour. As boardbunny said they'll probably give you a list of what to bring.