I have restored some period buildings that had cloth wall coverings and have been surprised at the lack of obvious soot stains except around gas wall lamps (unusual) or fireplaces. Instead the colors seem to have yellowed, very similar to a place where people smoke cigarettes inside. Most of these rooms would have used kerosene lamps with glass "hurricane" lids.
Of course cleanliness was next to godliness and such and part of the reason for cloth was that it could be taken down and washed along with the walls underneath. Indeed spring cleaning once included giving the walls a good scrubbing at least once a year.
Wall paper is harder to tell as it kept getting new paper and even when the time is taken to peel layers off you can't tell what is dirt or sun yellowing and what was from the next layer's glue.