Union Pacific AC4400 #6344

I recently purchased MTH's version of UP #6344. I really liked the paint scheme, and thought it would be a cool peice to add to my collection. I sometimes run my trains on a modular club layout at local train shows; so I figured I'd better do a little research in case I'm asked about this locomotive. I've heard it called the "gray ghost". I also found that it was formerly owned by Southern Pacific, and was aquired by Union Pacific in the merger. I have found very little info on it other than this, with the exception of photos. Below are some pics of it with what appear to be 3 different paint schemes. Not sure about the 1st photo, but it looks to be the SP paint. The 2nd is the "gray ghost" paint scheme. The 3rd is the Southern Pacific with UP numbering. The 4th and 5th photos are in standard UP paint. I'm wondering what paint scheme this engine is currently wearing? Also, any info and history on this locomotive, paint or otherwise, would be appreciated. Thanks!