I have also seen similar centerpieces that use epsom salts instead of sugar. You could also sprinkle a mix of pearls/gems. Sand (or sugar), faux pearls, a 3 candle. An easy DIY wedding centerpiece idea.
An interesting unity idea! Instead of mixing colored sands in a jar or a unity candle, this couple mixed paint on a canvas during their ceremony. But maybe add a monogram in tape, and tear the tape off after the paint dries?