When あなた graduate from Hogwarts, あなた don't wear the house colors. Do あなた see any of the trio wearing their house Colors(色) during breaks? No, Dumby just likes blue.
Who the hell is Domb;edore? And I don't think anything called griffindor is mentioned in the book. >.< Dumbledore probably just likes blue. あなた don't wear your house Colors(色) when あなた graduate.