use food dye to make ice cubes. Then put them in a glass of water-voile. Would be good for a party. Rainbow ice water - Taste the rainbow! - this would be cool for Christmas drinks. Red, green and edible glitter!
If you want to ad some whimsy to a traditional event, you should try Over the Rainbow Pancake Breakfast. This event would tie in very nicely with St. Patrick's Day as residents eat their way through a rainbow of pancakes.