Even in modern Japan, most grooms wear the traditional black and white ensemble on their wedding day. On top of the common under garments, he will wear four layers:
an underkimono (called a nagajuban) with some sort of decoration on the back.
a solid black kimono with five family crests (called a montsuki) with obi
a pair of black and white striped pleated pants (called hakama).
a solid black jacket with the same five family crest (called a haori). The lining of this jacket will have an elaborate design, often matching the design on the nagajuban. The haori is not worn with a belt but is loosely tied in the front with a white pom-pom'ed tie (called a himo).
The footwear is a pair of white tabi socks and white square-toe'd zori sandals. The groom might carry a fan for photos.
As with the bride's attire, these ensembles are quite elaborate, expensive and worn only once, so most grooms will rent them for the day.