We've seen this a lot with the unity ritual during the wedding ceremony. Initially, couples lit a unity candle, but soon that gave way to other unifying symbols, such as unity sand or unity flowers. One of the cooler new takes on the unity ceremony that we've seen - and loved - lately is the unity painting.
p.s. One word of caution: of course you'll want to be careful not to get paint on your wedding gown; we would NOT recommend finger-painting, no matter how much your and your fiancé's inner children like it! ;)
image sources: Chris Diset Photography, Cloud Seven Photography, Etsy, Gracenote Photography, Pinterest, TWA Photo and Wedding Chicks