Hmm Once when I got a potion, I had the villager drink it and he died instantly.
I'm guessing it was red.

ALSO- I think the paintings might be in both caves. I've gotten that twice and I picked the one with the glint of gold the first time, and the one with the cry for help the second time, and both times I remember reading about cave paintings as a result.

ANNND- For the one where the villager finds the big pearl, just fyi, if you let the villager keep it to themself, he or she gets all stingy and mean or something.