new to cruise,
ARRGGHH!! I'm so confused. You are not helping the new cruiser here. There are so many varied opinions about what is appropriate, and what's not. I chose Celebrity because of it's reputation of being somewhat upscale, and I will be disappointed if there are jeans in the dining room on formal night. I'm really looking forward to dressing up, and not looking like a boob because I'm the only one wearing a formal dress.
Overall, Celebrity is the dressiest cruise line that I have ever encountered. Many passengers, especially ladies, tend to dress beyond the prescribed attire, especially on informal and casual eveings. It's quite common to see ladies in fancy cocktail dresses even on casual evenings, for example.
Your formal dress will fit in quite nicely on Celebrity's formal evenings. For gentlemen, white tie and tails would be excessive, but ladies have no worry.