I used the robes to the pool since some days it is cool outside..here is the key word..layers..shortsleeves are okay but you might want a coverup..the a/c is set for a full show room of people, temps vary day to day..just like at home..remember it is cold we had rain and snowflurrys in canada in June two years ago..
We also used the robes for going back to our cabin after using the spas/hot tubs, it is hard to get dry/warm/dressed out in the cold, easier to put the robes on. Some people wore track suits as well.
The inside temp was quite pleasant. Most of the time I just wore a long sleeved top/blouse and if I knew I would be going outside, took my jacket with me (the pockets had hat and gloves!!). Glacier Bay and College Fjord were cool/cold days and most people had jumpers on inside as well as jackets/coats outside.
Formal nights many men wore coloured shirts not just white. From other reviews and my own experience clothing was fairly casual for the whole week. Mostly suits and ties worn by men and not many tux's, couple of men wore turtle necks. Most women dressed nicely (what you would wear to a wedding) but no ball gowns or the like.
On the Sun last May, most people were less formal than we saw in the Caribbean, probably Sunday best for formal nights. Long sleeves were warm enough inside. It was very cold the week we went with a constant cold wind, so take something with a hood to block the wind.