Overall, I (solo traveler) had a nice time. However, midway through the cruise I went to the Observation Lounge for a drink after dinner. The server came over to take my order, but then reminded me of the dress code (see below). I was extremely confused as I was wearing a white blouse, black skirt, and heels. I asked him to clarify, but he just repeated himself. After bringing me my drink, I felt so uncomfortable that I left and went to the reception desk and asked the person on duty if what I was wearing was appropriate and she said yes. It's unfortunate this occurred, because it tainted the whole experience. I felt like I didn't belong there. I did reach out to the cruise line and they were empathetic and apologized, but I don't know if I will cruise with them in the future.
Per their website, Regent's dress code after 6:00 PM reads in part "...the recommended onboard dress in the evenings is Elegant Casual. Dinner dress for ladies includes a skirt, or slacks with a blouse or sweater, a pant suit or dress..."