It may be because the P60 is more tightly focused than the P61.
My P61 looks noticibly whiter than the P60 though. The P61 is not as tightly focused but it puts out alot more light, it's hard to tell on a wall 5 feet away. If you go to a large dark room, the difference between the P60 and P61 is enormous.
After about 10 minutes or so of use, the P61 starts to equalize with the P60 and eventually the P60 looks whiter.