When I’m trying to set up a train line the 2nd station on the Train Line window shows up in a Maroon color and will not start running trains. I’ve tried reversing the order of the stations but the issue is the same no matter what the order. The 2nd station added always is maroon on the Train Line window.
I had this same issue, however I solved it by rebuilding the entire rail line. My guess is that I didn’t have something connected just right. A slightly less costly way to deal with this would be to detach each of your rail lines from the stations, and then re-attach them, making sure you attach them in the correct orientation. Also if you get into the signaling view you should be able to see if there is anything obstructing your rail line. I know I had an issue where I didn’t have a bridge high enough and it caused my trains to not run. Unfortunately I can’t get the game to load my save right now, so I can’t do any playing around with the trains to try to recreate that issue.
I can confirm this works, but I solved it by rebuilding just a couple of section of rails.
In my case I had an excisting, working line with 4 stations. I then changed station #1 from small to large and had to rebuild part of the tracks. Upon doing so, the station #2 I was trying to reconnect to kinda sorta got shuffled a tiny bit so all the road and rail connections were messed up. I had to move the station back into place and reconnect the roads. The rails looked like they were neatly reconnected all by themselves, but I guess it wasn’t so. So I just rebuilt the last sections of rail coming into and going out of station #2 and then everything was working again.