We're going on our 4th Carnival cruise this month and the wife finally talked me into the formal dining. I checked Carnival's FAQ and they listed a suit as formal wear, not necessarily a DARK suit. I planned on wearing my grey suit (thats the only one that still fits) am I going to fit in?
The right to prescribe proper attire always rests with the host --in this case, the cruise line -- so whatever the cruise line prescribes is the last word as to what's proper. I have cruised only on Princess and Celebrity, and both of those lines explicitly stipulate a "dark suit" as an alternative to a tuxedo or dinner jacket. Nonetheless, I have heard pretty consistently that Carnival is "less formal" than Princess or Celebrity. If Carnival specifies a "suit" rather than a "dark suit," your grey suit will be fine.