Buffy loves the heat, and if there's any hot spots around the house (like sun spots), you'll find her sleeping on them. Willow, on the other hand, who is a dilute tortoiseshell (with light grey), she HATES the heat and just can't handle it. She prefers the cooler weather. It's odd, you'd think the black ones wouldn't be able to handle the heat and cooler ones would be fine ('cause lighter colors reflect heat), but it's the other way around in this house. Maybe it's the coat density thing: Buffy is a shorthair while Willow is a longhair. Hmm...