1. Silver Chocobo
The most infamous chocobo rumor is the Silver Chocobo. Feed and breed two S-Class chocobos, and there's a small chance you'll receive the Silver Chocobo. This chocobo is capable of travelling underwater (and in space, depending on who you ask).
D. Peck boasts a way of getting the Silver Chocobo. Mate two maxed out (170 speed) Gold Chocobos (with a speed of 170) with a carob nut, then mate the baby with the one of the maxed out chocobos with a zeio nut. Ensure they are at class S, and the baby chocobo has the same speed as its parents.
2. Rainbow Chocobo
The method of obtaining this chocobo is unknown, but it is rumored the Rainbow Chocobo is capable of flying in the air (just like the Highwind!).
The following details have been contributed by Shane: With a white chocobo, travel under the Swamp adjacent the Mythril Mine and you'll engage the Rainbow Chocobo as a boss character. Defeat it, and the Rainbow Chocobo is yours.
3. Wooden Chocobo
This rumor is weird. Visit Wutai, steal Lord Godo's underwear and run into the nearest forest. Inside you will find the Wooden Chocobo.
4. Blue and Red Chocobo
It's been suggested that the Red and Blue chocobos are obtainable. You can find Red and Blue chocobos in the chocobo races, so this rumor has some validity. No method is known on how to obtain these chocobos.
5. The Invisible Chocobo
This has to be the worst rumor of all. Travel on the World Map, constantly tapping your button as if you were really climbing a chocobo. If you're lucky, you'll accidentally climb on top of the Invisible Chocobo.
Update (August 2000): D. Moffatt has provided some input on this particular rumor. If you pop the PlayStation CD cover open while having a chocobo beside you, it will 'disappear'. What has really happened is the chocobo's image is gone but the chocobo itself is still there for you to ride. Cheers Mr. Moffatt.
6. Purple Chocobo
Details on the purple chocobo have been gratefully provided by Carolyn. The purple chocobo seems to be impossible to get. Go to Chocobo Sage's house and go up to the green Chocobo. Release the Chocobo by smashing the glass and it will run away. Chocobo Sage will chase after it and his purple hat will fall off. Steal it and go back to the Chocobo farm. Give the purple hat to a gold S class Chocobo when you are feeding it sylkis greens. Get the gold chocobo to mate with another gold Chocobo (S class) and make it produce a purple Chocobo, using a zeio nut. This purple Chocobo is extremely amazing. Remember how Teioh's speed and stamina is always higher than yours? Well this Chocobo's speed and stamina will always be higher than Teioh's at the start of any race.
7. Grey Chocobo
Rumor distributor Eecetera@aol.com believes a grey chocobo exists in the game. To get a grey chocobo you must mate a white and black S-class chocobo with a zeio nut. The grey chocobo can go underwater, just like the white chocobo.