As'salamu Alaikum dear brothers,
Jazakum Allah Khayr. It is interesting to see the "black dogs" in the Hadiths, because black dogs in Arabia at time included:
1- The African wild dogs, which eat their prey alive.
2- Possibly hyenas. They do belong to the canine species. Their claws are dull, like all canines, and they only fight with their jaws. Cats have curved claws, and they fight with their four claws and mouths/jaws.
These mentioned animals are also desert animals. So black dogs definitely include those, in my opinion. So most probably, the worst of the dogs back then were probably aliased as "black dogs". Like our pitbulls of today (banned in England), the worst of the dogs back then were probably referred to as "black dogs" in the Middle East. I don't think this was due to the actual color (like black=evil), but rather due to the fact that the much darker dogs were certainly the most feared if we include the African wild dogs and hyenas.
This makes perfect sense for me.
Take care,
Osama Abdallah