one in a million, minor thing...and probably something to do with the way cutscenes are made,,
I created Remove Curse potion (which seems to turn cauldron white for much longer than Health Potion) only couple of minutes before Lindara showed up to trap Briley in pentacle thingie. When cutscene with Lindara starts... white cauldron turns immediately black and after Briley is freed and returns to same spot, cauldron turns back white and only cools down next morning...
Basically one in a million chance that cauldron will be white when that cutscene kicks in... so nothing to fix here really...
Now back to playing... :)