They attract the heat right into their coats.
Weather has been a big topic in New Jersey and across the country this year. June and July were very wet and cool around here while Seattle has hot and dry. Now all of the sudden it is blistering hot and being near the ocean, really humid.
Black rabbits really feel the heat. It seems to absorb into their coats and cause life threatening conditions for them. They will pant with ears shaking and mouths open. Sometimes they lay stretched out on their sides, flat out. Their ears will feel hot and they will be breathing fast to try and cool themselves. Mist them with cool water, put ice on their ears, give them a frozen water bottle or ceramic tile to lay next to. Clipping the bunnies down helps to make them more comfortable for the summer. When they are really in distress, I have seen people put them in a cool bucket of water. There goes a show coat but the bunny's life is saved.
When you are at a show, you can hold an ice gel pack under their chest or against their ears to cool them. I have even used a cool can of soda if I didn't have anything else. You can also put those gel packs under each wire floor of the travel carrier to cool the cage wire without getting the bunny wet.
I feed and water in the morning or evening, leaving them to chill out for the rest of the day. I added a mister hose last year and it really makes a difference to the air temperature. If you can, but them in air conditioning or in a cool basement. Stay cool everybunny.