Due to M7 cars emplacements, it is impossible to select a livery in Timetable mode. The problem is that M7s number of cars appear as liveries but no downloaded or created livery is visible. East Coastway trains (Class 377/4) for exemple do not have a such problem though. I don't have M3 EMU DLC but it may have the same issue. If you didn't know, that issue is probably there since LIRR DLC came on TSW2.
This, I just spent about 7 hours working on a new livery for the m7 and just found out I can't equip it in timetable, for now the only workaround seems to be by creating a scenario, hopefully it will get fixed.
Unfortunately the M7 livery selector is set up to choose length (which changes the services available) rather than livery
