PlayStation Found It!

trainbow is not a myth

 

You just need to "Get Lucky".

 

out of the three times ive spawned in on the route, ive seen it

 

I got dropped into Trainbow when I did Tricky Tunnels, so my trophy shots for completing that scenario and for completing all scenarios have got that added rainbow zing.

 

Just saw it again when starting at at Pancras. Interestingly, it has always appeared to me coupled to another unit

 

I had Trainbow as the first train to get in when I played the route for the first time

 

Not seen it yet. So yeah just waiting.

 

I got it on the first scenario where you do St Pancras to Strood !

 

I got it last night!