I'll be waiting for those pics.
I'm good with the 'big cat' thing. Don't know where your buddy's ranch is located, so it is quite possible you saw a 'cougar'. You lose me on the black/dark part though, unless you saw a dark jaguarundi.
Either cat will be most difficult to get pictures of. They just don't hang around one area long enough unless they have a den there for some reason (litter of kittens or trying to establish a home range).
You'll get a lot grief over any claims of seeing a 'black panther'. I won't contribute, but I am in that camp.
Hope you get some pics, would love to see them. Good luck Sir.