Muck

What colors should we paint our railroad car trucks and wheels?  

Many variables to that question - environment, maintenance, era, age and usage.  These examples are old Denver & Rio Grande wheels set into restored trucks.  Look closely and you can see a variety of color and texture on the same wheel sets.  Like the track, the metal wheels can even host the growth of moss/mold/mildew, as visible on the right wheel in the second photo below.

Two trucks of the same car (this photo and second one below...

...left wheel is much greasier.)

A variety of rusts and grime on these couplers

Rust patterns and colors on this bolster.