Polly S makes a very accurate tie color for US railroads called...."Tie Brown". It's been a standard in the Model RR world for a while. I would imagine that European ties would be similar, at that time. Later they pioneered concrete, but not under Karl. Ballast colors vary widely- they are whatever color of gravel the railroad chooses to use, overlaid with pollution. Usually it's pretty contrasty to the surrounding terrain as it's generally imported from somewhere else, at least in the 20th century. If it's a well traveled line; and a beast like that probably wouldn't be sent out onto lighter rails, there's nothing growing in the right of way.
It was really common for railroads to use coal clinker from the ash pits of their operational yards, because they had a lot of it. That would be a nice dark grey with a shine to it. A decent way to get that is to bust up a bag of charcoal; not Kingsford because it has wood fibers in it, but Mesquite or something like that. It usual that the rails and ties are pretty close to the same color, except for the railheads (they're the guys in bermuda shorts holding cameras) but it's all a product of what gets blown all over them.
I model RR'd for about 30 years before I gave the space up to other things. Miss it a lot.