The problem has to be with your monitoring. All XDCAM Transfer is doing is re-wraping the files to MOV. There is nothing in that process that can cause any change in the essence the file.
FCP and the computer monitor attached to it, is inherently NOT color accurate. Quicktime 7 Player itself has an Enable Final Cut Studio color compatibility check box which impacts gamma. The default gamma between Leopard and Snow Leopard is different.
What ClipBrowser or XDCAM Transfer display may not be the same FCP or Quicktime. You need to know about color calibrating with the two OSs to even get close and a computer monitor still can’t be accurate for “broadcast.” In addition, using something like Matrox MXO series which can at least get a 2nd non broadcast monitor (Computer or HDTV) close to accurate can help.
This should be a MUST lesson with Video editing with NLEs before anyone takes on professional work which needs to be remotely accurate for use on a TV or Broadcast.