I agree with the above and would like to add recommendations for jetted pockets. As far as I have understood, there is a much greater freedom for individuality in daytime formal wear. However, these are some of the guidelines I have picked up:
Wear grey, heavily patterned trousers (large patterns preferable).
Wear a double breasted waistcoat. It can match the coat, but certainly does not have to.
Wear a white collared shirt.
The coat, black or oxford grey (herringbone...