I understand that the standard UP freight car lettering changed from white to yellow after 1948. I would presume that any given car would not have been so repainted after 1947 until the regular time arrived for routine repainting would have arrived, which could be a date considerably later than 1948. I do not know what the UP's usual chosen interval might have been for such boxcar repaints, but again (presuming, of course!) if a whole class of cars were last painted/ rebuilt in 1938, then they might last well into the 1950's, even to retirement, white lettering and all still intact?

It is difficult for me to discern dirty white from yellow on B&W photos.

Denny
Denny S. Anspach MD
Sacramento