Great feedback, thank you! Good point about the buttons at the end of each level. I think I nearly misclicked one during my playtests, so I'll definitely improve that. Disabling them for 1-2 seconds seems like a good solution.
I did implement a "random colours" mode for the tracks that does as you suggested, but found it a bit chaotic to balance against the other settings (number of tracks, spawn frequency, number of enabled colours, train speed, etc). Might revisit the idea though.
Thanks for playing!