Wouldn't that be a Coat of Arms rather than a Crest? A crest is a symbolic material posession passed down from generation to generation, such as what Lucca said in the beginning of the game "OMG isn't that HAIRPIN the Guardia Family Royal Crest?" or something like that.
If it is a coat of arms, which it most likely is, then the two colors represent joining of families, and the dragon represents power of the royal family. I know this because my family's Coat of Arms is a green background with a blue stripe and a Large Tree, which symbolizes eternal earth, a river, and a motherlike figure (the tree).