It is quite normal for the Xenon's to appear much brighter than the usual Halogens. When you observe the color difference are you looking at it from straight ahead or off to one side. Try looking at it from one side, then the opposite side, then straight ahead. Perhaps being slighly off axis will give one headlamp a different appearance than the other. Other basics like making sure both headlamp lenses are both clean. The Xenon's have something of a "self-aiming" feature. If it is skewed it might look lop sided. (just like if halogens are mis-aimed) Since it looks normal while driving I would guess everything is fine, it just appears different based on perspective. Just a guess?