Tropical Night is Tuesday.
To elaborate on what my wife (danicaw) said:
We had 6:00 reservations for Palo and we both dressed the way we would have dressed for Palo on any night. Then we went back to our room and changed into our tropical clothes, had some photos taken, then went to our regular dinner seating at 8:30 for an extra snack and dessert
I did see several people at Palo in tropical clothing. (A tropical shirt with a sport coat over it, for example.) I think classy tropical wear at Palo would probably be OK, but I personally wouldn't feel comfortable going to Palo in my tropical clothes.