My Xenon blew out and the dealer replaced the light unit (more)

with a brand new one...now the bulb turns on to a bright blue in the begining as usual when it fires up, then fades to a yellowish tint...It is very noticable compared to the other side which burns a pure white with a blueish tint...the dealer then switch it with another brand new headlight assembly and bulb and it still does the same...the dealer called MBUSA for help and now tells me that the bulb needs to burn for a week in order to change to a pure white color...does this make sense to any of you??? I didnt know that xenons needed time to 'break-in'.....do any of you new CLK owners have this problem??? Please help!!!