I premise that for me it's not really a problem but since someone pulled it out I thought of a couple solutions:
1) probably not applicable because of publisher restrictions - add an extra colour, that can't be used by anyone, and you can choose to force yourself to that colour. Opponents see you of one of the usual colours and you see it in the scoreboard, but the trains are always the same. Not the best solution, but as an optional one, it's still better than nothing.
2) better and seems more likely to be applicable: have your trains slightly glow or bordered with a thicker/different colour line to highlight them. Still optional, since it can be annoying for someone, but seems like a solid solution
1) probably not applicable because of publisher restrictions - add an extra colour, that can't be used by anyone, and you can choose to force yourself to that colour. Opponents see you of one of the usual colours and you see it in the scoreboard, but the trains are always the same. Not the best solution, but as an optional one, it's still better than nothing.
2) better and seems more likely to be applicable: have your trains slightly glow or bordered with a thicker/different colour line to highlight them. Still optional, since it can be annoying for someone, but seems like a solid solution