Hi Coke,
The Tiffany's, as reported by the Pueblo Paper (Ron Rudnick did the research) were reportedly white, as mentioned in the article, not yellow, not green, white.
Mal may have gotten his chip from the last known Tiffany, which was used as a shed in Leadville Yard (since demolished in a "Yard Cleanup"). The UP Refrigerator Line cars were painted a straw yellow according to research, just like the UP built bobber cabooses. The Bobbers had a red lettering, bye the way.
My opinion is, give the customer what he wants, he's the one paying for it, and other than the Pueblo article, nobody recorded what color they were delivered in.
Rick Steele