you should worry about bottle temperature more for the health of your engine than the appearance of your purge. when nitrous stays below its optimal temperature, it can lean out your motor and cause some serious damage. that's why you want to use a bottle heater during the winter. but as far as the purge goes, naturally (duh) since nitrous is very cold, it would be more apparent when purged in a higher temperature environment. it is also affected by your purge tube's bends, bottle pressure etc.