Hi everybody, I bought for my WR450 2003 an head from 2005 (it is cheaper). Everything is the same, with small difference. The 2005 has AIS system ports. The problem is that 2003 and 2004 heads have valve lifters with different colors (mine are blue), but 2005 head have only yellow. Can someone explain me what is the difference between valve lifter colors and head on WR450? Which is different in lifters with different colors (blue, yellow, red, black, green)? Can i use blue colored valve lifters on 2005 head? They fit and move well. Thanks in advance.