What determines the red vs. blue ends of trains?

[JasonC]

Double-ended trains seem to have a red light on one end and a blue light on the other. What determines which end is red vs. blue?

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[Astree]

If I'm not wrong, red is what was the back of the train on its last move

[JasonC]

If I'm not wrong, red is what was the back of the train on its last move

Hmm; all those trains effectively have the same route though (as far as turnarounds and travel direction go -- each of those trains will leave the pictured stations and arrive back at one of those stations in the reverse orientation, after one stop) and those tracks are one-way, they came in to the screen from the right.

[Jap2.0]

I believe "front" and "back" may be determined by the order you build it in - not entirely certain, though.