Do you happen to have any custom liveries in the Livery Editor? It might be worth double checking, since there could be a blank project that was saved and is now showing up on consists by random chance
They do. The only exceptions for german trains not applying custom liveries at AI are the ICE due to licensing and the SKA Talent 2. All the other locos having the option of being in the livery editor get random custom liveries on AI.
Because ICEs are not allowed to take part in custom livery competitions due to licensing which was said by DTG so I suspect it is the same why the ICE and the BR 101 wont appear with custom liveries in AI traffic. And for all the rest: I just played the game for a ton of hours.
It wouldn't be hard to check. Create one or two new liveries, leave them completely white, spawn a couple of times at a busy place and see if you see any greyish rolling stock, which seems exactly what happened to OP. From my experience both locos and freight wagons do sub (ONLY THE BRD VARIANT OF THE ROLLING STOCK - also as a substitution on older routes), I am almost completely sure pax coaches can spawn with your livery as well. I don't know about the Talent. The trains included with BRD are (I believe) the first german trains which will randomly spawn with your own livery. My livery randomly spawning on freight wagons in timetable