Grooms wear waistcoats

The best man, ushers and my dad are all wearing blue waitscoats to match the bridrsmaids dresses. My H2B is wearing a different colour

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They can wear the same or different if you chose.

All the men in the wedding party wore a grey three-piece suit. Boy and best man wore champagne cravats, the others wore ivory.

There is no 'should' about what you wear - it's entirely up to you how you want the boys to look!

Ours are wearing all the same but bestman, ushers and dads will be wearing the carvats to match bridesmaids and OH wil be wearing the colour of my dress

It's entirely your choice. We had all matching waistcoats but the groom wore and ivory cravat and the rest of the men wore the same colour cravat as the bridesmaid dresses and rest of the colour scheme. I think a lot of people do it this way because traditionally (or in the olden days or something) the groom matched the bride