I love this idea. An envelope guest book. You just take a store-bought scrapbook/album and glue envelopes into it. Lay out colored pieces of paper for guests to jot notes down on, and then they can place them in the envelopes.
The groom should always look distinct from his groomsmen. Here, the groom wears a suit jacket and traditional tie, while the guys don vests and bowties. Just without the different color suits. One color