I recently attended a black tie dinner on the beach in Acapulco. Black suit, light blue shirt, flash silver tie. I also have a dark blue (nearly black) shirt that I sometimes wear.
A dinner shirt doesn't have ordinary buttons ... although you could get away with it. Dinner shirts have covered buttons, or studs.
A dinner suit also has buttons which are covered in the same fabric as the suit, so they don't show ... and the lapels are a different fabric from the suit itself.
With a dinner suit, a guy might also wear a cummerbund to hide the join between his shirt and trousers.
His wife and family went down to dinner in this hotel and Laurence Olivier asked the maid to tie his bow tie and the shot ended with this nubile female, dressed in maids uniform, standing in front of him tying his bow tie.
The daughter was sent back upstairs to see where "daddy" was, opened the room door and there was "daddy" screwing the maid.
This thread reminded me of the film...."the Betsy"
Just to confirm - for something as formal as this, partner needs a proper formal dinner suit, which usually includes a dress shirt, an ordinary shirt is not suitable, and he will feel consoicuous.
I wouldn't worry too much about a 'real' bow tie, but make sure it is black. He will need cufflinks for the dress shirt cuffs, and he must wear shiny black shoes - cleaned!