I love Black Chocobos: As you can see from my name.

To get a black Chocobo you'll need to breed a Blue male/female with a Green male/female. Make sure you train the parents to be "S" class racers. Again, you will need a Carob nut.

To find Carob nuts. They cannot be bought, they must be stolen from an enemy called Vlakorados....you'll find him near Bone Village. If you don't know which one he is...he's the red raptor/dinosaur looking creature, and he's tough to beat. Make sure you have "steal" materia equipped on one of your characters armor. Once you steal it, you can just escape...you don't get very much AP or GP from him...you just need the carob nuts.

I recommend alot of time at the Gold Saucer...You will need to race to make your Chocobo strong and be in the "S" class...