Gerald Grudgings
Noted re seated passengers. Will be a bit controversial.
What needs to be done depends on the period. If since the 1960s modernization then the points are valid. In with modernization came quality lighting, passengers wore brighter colour clothes, the windows are larger and much can be seen.
I model steam in the 1920s, however the scene remains up to the ’50s or so. I remember steam from around 1954 onward. Most passengers wore dark clothes, for after a long journey the first thing needed was at least a wash, perhaps a bath, and clean clothes. Add to this the lighting was very basic, in a Mk1 compartment coach would be 4 x 24v golf ball pearl bulbs in a white shade, a similar light sometimes on the ceiling. It was only just enough to read by, and from the outside all you could see of passengers was basically silhouettes. The modern RTR coaches with lighting have it too bright. When viewing a train after dark, yes, you could see it was lit, but the light did not “spill out” from the windows. If you can still buy grain-of-wheat bulbs they are probably about right, the LEDs are way too strong unless you can “turn the wick down”
So in steam era the passengers were well obscured, it would be possible to fit otherwise inferior as they are hardly seen in any detail.