Yep, that's one thng the Santa Fe and UP shared in common - silver truck on their road engines. This lasted right up until the merger and now we're seeing BNSF units with silver trucks again, a nice move. The only engines I'm aware of that didn't routinely have silver truck painting were the blue and yellow freight F units and most switchers. The Santa Fe was pretty good about keeping their units clean up until about the early 70's, when the rot set in, so that's about when you start seeing units with enough rust and crud that it's hard to tell their trucks were ever silver.