Also on the flying chocobo "debate" <.<...
Yellow Chocobos are the basic type, basic speeds no special abilities, easily tamable which is why we have them available to rent in games and the MMOs as well.
Blue Chocobos are able to cross rivers and streams, and when used as a companion in battle they are magic users.
Green Chocobos were able to climb mountains in VII, but that was the only occurrence. They are typically found in the wild and are hostile towards the player, but when tamed and used as a companion in battle they are also known for being healers with the unique cure "Choco Cure" as well as some other unique abilities in various games.
Red Chocobos are less common in the games, and are usually considered rare chocobos depending on the game. In FFIX they were able to traverse mountains, while in FFXII it was one of the rarest spawns in the game replacing one of the black chocobos, and is one of the most powerful enemies in the game. In battle they are generally known for their high attack speed and damage, though in Theatrhythm they are known for being the weakest.
White Chocobos are more rare than the red chocobo, and are basically an upgraded Green Chocobo being a more powerful medic.
Black Chocobos are most notable for their
ability to fly in some games, though not always the case. In FFIV they were able to fly over water and forests, but not mountains, and were only able to land in forests. In FF Tactics they were also able to fly. In FFV they were able to fly over mountains, but not snow capped ones. In FFVII the black chocobo was simply the offspring of a Blue and Green, merging both abilities together letting the Black chocobo cross both mountains and rivers.
Gold Chocobos are the rarest and most valued chocobo with their ability to fly like the Black Chocobo. In FFVII the Gold Chocobo was the only version able to cross the ocean, giving the player access to the Knights of the Round summon. In battle the Gold Chocobo is a more powerful Red Chocobo having higher attack damage and speed.