Ya your local hobby shop will have a number of different colors of paint in spray cans (I like Tamiya myself). The entire seating section on those cars is removeable, just take it out and paint it whatever color you prefer. Tan or a dull yellow would be good, or even primer gray.
Apparently Walthers is going to come out with a 1955 Empire Builder soon, similar to what they did a year or two ago with the Santa Fe Super Chief.