Step 1, obtain the lure & some mid priced greens
step 2, hire out all stables
step 3, get carob nuts from red dragon/dinosaur thing near bone village & get a Zeo Nut from a goblin (goblin isl is in NorthEast of map)
step 4, Capture a "Great Chocobo" from the Mideel area and a "Good" from the peninsula near Corel prison. Make Sure there Opposite Gender of course.

Step 5, SAVE BEFORE mating them. because otherwise you'll have to wait or get fresh ones if you don't get the right kind of kid.XD This should give you green or blue.

Step 6, once you have a green & a Blue feed them about 10 Sylkis Greens each to up there stats.
Race them untill you get class A then mate them for black.

Step 7, (that most ppl don't seem to know)
From Icicle area and capture a "Wonderful Chocobo" whose sex is opposite that of your Black Chocobo. Feed both 10 Sylkis Greens & race them until Rank A.
Mate these two with the Zeio Nut.

*Poof* Gold chocobo ^v^ *wark*

[note] i don't think raising the ranks is essential but it definitely raises chance of getting the desired colour.

what he said