Black Tie
One of the joys of wearing a suit is showing your ability to express yourself within rather narrow constraints. When wearing Black tie: this is much less the idea. There are some ways in which one may express himself, but one does this through even more subtle means. As with everything, trends have come in and thus many of these rules are merely guidelines, though some remain hard and fast.
First and foremost is in the name: the tie. It’s not black tie if you are not wearing a black bow tie. The trend has been to swap out other colors of tie and vest. You can wear a pre-tied overly shiny straight tie with a vest of the same fabric that is either gold or pink or some other outlandish color, but the statement you are making there is: “I’m going to junior prom.” As an adult the only excuse for wearing a clip on is if you are working security. Therefore, you should always wear a black silk bow tie[1] that you have tied yourself. In the event someone is not adhering to this rule you should always remember that it is inappropriate to correct him, but you should certainly judge him silently.
As for the vest, there are a few different options. A cummerbund is perfectly “acceptable” but I will certainly judge anyone wearing one silently, and you should too, as they are terribly unattractive. As of late there has been a trend to wear no vest or cummerbund. This looks perfectly fine, though if you want to adhere to the classic tuxedo look (which will always impress people), then I recommend a vest cut low in the front to show the shirt. The vest can be backless or backed and can have lapels or not. Whatever the case, it should always be black and should be made of either silk or a silk and cotton blend. Given how hard it is to get a vest that meets those requirements, it is also perfectly fine to get one cut from the same cloth as the rest of the tuxedo. Also note that while one never buttons the bottom button in a suit, every button is buttoned on a tuxedo vest. While we’re on vests, now seems as good a time as any to bring up that a wrist watch is fine with a tux, though a pocket watch just adds an extra layer of class.
Any shirt worn with a tuxedo should be made of 100% cotton, require studs instead of buttons (at least where visible), and require cuff links (though weirdly enough: a double cuff is not the ideal in this situation.) There has been a trend to have a flap over the buttons to hide them instead; that is fine though not the classic look. While pleated shirts are what most of us associate with tuxedos, they are by far not the most classic shirt. Pleated shirts are like cummerbunds in that they are “acceptable”, but impress no one. Instead a shirt with a textured front will look better, though what has never ceased to amaze is a full formal shirt. A full formal shirt has a bib at the front that is so thick and starched it always looks perfectly flat. More than that though, a full formal shirt has single cuffs of the same thickness, and a detachable collar (also made of cotton and starched to the point that it might as well be made of cardboard.)
Shoes should consist of black derby oxfords, with no broguing, and nothing else. Traditionally they are Paten oxfords, but if they are textured in a way to look tuxedoish, they can be a nice form of self expression. What you should however not wear are plain oxfords, or anything with stitching of any kind at the toe.
The coat and pants are where things are often shaken up. What makes a tuxedo are the silk accents on the lapels and down the pants, as well as on pockets. They are always black silk, but there have been trends of inserting color into the rest of the suit itself. This is fine, though a tuxedo should always be made of wool. Traditionally the suit is black. Single breasted, with peaked lapels, jetted pockets, 1 button, and a ventless back. Not adhering to these rules too strictly is fine,[2] though the more formal the event, the more I recommend sticking with black (Winter time is always more formal). It is worth mentioning that the ventless coats on tuxedos seems to have been forgotten more than gone as a style trend. As a result you may find it hard to find a ventless coat.
As far as accessories are concerned, the most obvious are the studs and the cuff links. They should come in a set together. traditionally they are silver or gold (should be real silver or gold, not steel if possible) and filled with onyx or mother of pearl. There are some other options, but you cannot go wrong with the classics. Though if you can really find it, electrum is my favorite. If you wear a watch, the metal should match the buttons and cuffs.
A boutonniere is a nice touch, though if you are going to wear one, it should absolutely be a real flower. Note it is also best to keep it in a boutonniere holder instead of a getting one from a florist to pin on. again, the boutonniere holder should be made of sterling silver or gold[3] to match the rest. If not, then a silk pocket square is just a little less showy. I would not wear a pocket square and boutonniere in order to avoid an outfit that is too busy.
Finally, we come to the outerwear. If it is cold, a coat is obviously necessary. An overcoat should always be black wool, and preferably double breasted, with exceptions being made for fur. It should also go to your knees or lower. Scarves and gloves worn with tuxedos are traditionally black or white, and made of silk and kid skin respectively. As for hat options, there is only one: a top hat. Top hats should either be made of silk, or better yet, beaver. I do however make one exception to this, and that is for a cowboy hat as a piece of my Texas heritage. any cowboy hat worn to a formal event should be a high quality cowboy hat.
[1] there are several bowtie shapes actually that are all perfectly acceptable
[2] Though one should remember that waiters and staff wear white jackets…
[3] If you want to wear cloths made for a gentleman, be prepared to spend like a gentleman…