For those of you who are going, and who have access to the Royal Enclosure, the dress code for men is very simple. Morning dress is the only option, and a top hat is mandatory. Nevertheless, this still leaves a great deal of room for manoeuvre. Indeed, the amount of variation possible in morning dress is one of its most appealing features and something that distinguishes it from White Tie, of which it is sometimes considered the daytime equivalent.
The basic requirements are relatively simple: A top hat, trousers, a waistcoat and a grey or black daytime tailcoat with tails which sweep round to the waist rather than being cutaway like an evening coat. With formal morning dress, the coat and trousers ought not to match. Indeed, the tailcoat ought to be a plain colour with, perhaps, a subtle herringbone, whilst the trousers are generally striped. The waistcoat can match the tailcoat but much more common is to have it in a third colour. Almost anything is possible, depending on the event, but most classic is buff linen or wool, especially if it is double-breasted with a lapel.
The top hat itself should also be either black or grey, but it need not necessarily match the tailcoat. Technically, the grey hat is slightly more informal but it is perfectly acceptably for the races which is one of the least formal events at which you might wear morning dress. As far as other accessories go, gloves used to be mandatory (as with any outdoor wear) but are now much less common, although they are certainly a nice addition. A pocket square is good, and a boutonniere is even better, especially at a wedding. A formal city umbrella is another classic accessory and is, in any case, a worthwhile addition at the races even in mid-June.
Any formal shirt and tie is acceptable, although contrast-collar shirts are traditional, as is a grey macclesfield tie. At Ascot, turn-up collars and (paradoxically) 'Ascot' ties or cravats are not really appropriate. Shoes should be plain black oxfords or, both more traditional and practical at the races, black chelsea boots.
If you are going, have fun; especially if you will be wearing morning dress. It is one of the very few occasions that remain when you can do so, and the atmosphere in the Royal Enclosure is really something to be experienced, quite apart from just enjoying a great day of racing.