Bridges what color?

[e-paw]

I would start with the question of are you trying to model a prototype or freelanced bridge. If it's freelanced the Sky's the limit . If it's a prototype or even Proto freelanced try to find some color pics or make a field trip to the location .
Where I grew up in Bayonne NJ. there were plenty of railroad bridges in all sizes, they were all black, weathered to various degrees it tones of browns, grimy blacks, and rusty colors.