If you want to feel comfortable and impress your host, determine what formal attire is expected based on the terms used in the invitation as well as the many choices available to you.
1. Black Tie is a common reference to a formal affair. If the invitation specifically states 'black tie' you WILL be expected to come in a tuxedo. You do not have to wear a black tuxedo - a grey tuxedo would be equally acceptable.
You may also prefer to add some color or distinction to your outfit by choosing a cummerbund, vest and tie that is a patterned or solid color. Choose a sophisticated cuff link and finish the look with black patent leather shoes.
The variety of styles available today allows you to customize your look with the cut of the coat, the color of your accessories and they style of neck wear. Depending on the event and your hosts you may determine if too much self-expression would detract from the evening. If you are unsure it is wise to stick with traditional black and white.
2. White Tie is the most formal dress request. It requires a strict attention to tradition and does not permit the guest to deviate from an accepted standard.
A White Tie event requires the men to be wearing a black, full dress tailcoat, wing collar shirt, white pique vest and tie. You may also wish to add such elegant touches as a top hat, cane and white gloves.
3. Traditional (or Formal) Morning Attire - Another take on formal wear for day time events is the traditional morning attire. The most formal suit is composed of a grey cutaway coat, striped trousers and grey vest with a wing collar shirt and ascot. Less formal dress would substitute a Stroller coat; lay down collar shirt and four-in-hand tie.
For non-traditional formal wear at a day time event you can wear a black or grey tuxedo or even a white tuxedo for warm weather events.
4. Semi-formal allows the guest to wear either a black or grey tuxedo or a suit. Seasonal appropriate colors can be used for day time affairs.