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There's no theme as such, but she's asked for all women to wear cream, and hats with feathers (which is hugely unpopular with the groom's family as 5 of them are vegetarian!) and all the men to wear black suits, cream shirts and top hats. This seems even more silly as both the bride and groom are well into their 50s and have had about 6 failed marriages between them!
The last wedding I went to had quite a good colour scheme idea, guests on the bride's side wore cream, yellow or gold, and the groom's wore blue, green, purple or lilac.