Celebrity has Evening Chic nights, and even jeans are acceptable on those nights.
Dress info from the FAQ on Celebrity's website:
EVENING CHIC
Each itinerary features one to two “formal” nights we call Evening Chic. Evening Chic means you dress to impress, glamorous and sophisticated in your own way, with a cocktail dress, skirt, slacks, or designer jean, an elegant dress top or blazer—some guests even pack a tuxedo or gown for onboard photos. The Daily program, delivered to your stateroom and available at the Guest Relations Desk, will be your guide to the correct attire each evening. If you do not wish to participate in Evening Chic, Smart Casual attire is acceptable for dining and theater.