I haven't experienced much difference in regard to humidity, although my turkey hunting doesn't encounter much of it. Red slate is a bit harder to condition than the others, but otherwise the variance is one of pitch and rasp. Black or Grey slate is the softest, followed by green, red and purple, and their pitch and rasp increase along that list as well. It depends on the pot as well, though. I have a green slate in a cherry pot that is raspier than my purple slate in walnut. They all kill turkeys, but if you want that stereotypical slate sound, you'll get what you want out of green or black slates. I've found red slate is a killer though.
