In contrast to the Night Vision option, could there be a setting that allows a token the vision option of purely seeing relative levels of warmth, to simulate the early AD&D Infravision? It would also probably require a checkbox option (perhaps defaulting to "yes," but could be manually turned off) that denoted warm-blooded status, so a token with Infravision turned on and within range would see a reddish rendition of the creature in question.