Just home from the Dawn, in the Caribbean-first timers on Silversea. DH wore slacks, polo, and sports jacket for all informal nights -formal night we went to Terrazzo which you can dress informal. Casual was slacks and polo. People definitely dress up on this ship and they were sort of strict about the jacket BUT many only carried the jacket on their arm, a lot more took them off the minute they sat down, we saw one person had a sweater as his jacket.
We thought it was interesting how "strict" everyone is with the man's dress but we saw many women in what I would say didn't follow dress code. For example, We saw short shorts (casual night) and yoga pants with a pullover fleece shirt (informal night).