Probably a missing entry in one of the smoke containers, just copy the color line from one of the others and add to the one with it missing, it's an error I've seen quite a few times.
Example:
Dave - May I use this thread to post a query about your Busch tram, front, middle and back?
I recently downloaded these, and all seemed from the DLS screenshot to have white roofs. However, in Surveyor and Driver, TS2010, whilst Tram front always has a white roof, the roofs of middle and back change colour quite randomly between black and white!
I have never seen anything like this happen before. Have you any suggestions?
I have sent you a PM about this a few days ago, but you have probably not seen it.
Dave - many thanks for your prompt reply. I'm certainly interested that you are seeing the same thing - and that it's not my computer! I will look forward to hearing from you if you manage to sort it out.