I wouldn't bother too much as there are only a few "avids" that dress up , the bulk of the dressing up is done by the activities and entertainment guys and gals. You will still enjoy yourselves on these nights "undressed". ... Neil.
One theme night as a rule caribbean night bright tropical shirt and chinos. she that must be obeyed has informed me a black and white night is also classed as a themed night. but its a formal night .if you need a nice bright shirt buy one on your first stop 10 -15 us dollars hope this helps enjoy.