Probelm with Chocobo raisings, help plz

Hey guys, im new hear so i have no idea if such a topic exists. So anyway, i read a FAQ on how to raise chocobos. I need a Blue chocobo, i got a green one but i keep troubleshooting on new chocobos (great chocobos B Class, if i dont get blue chocobo, i move up a class and see). But when i get a chocobo from Class B to A, i STILL get a green chocobo, i need a blue so i can make a black, if its possible not to use 2 different colored chocobos to get a black chocobo, PLZ TELL ME . I feed my chocobos the best greens, i feed them 10 greens, thats is alot of moneys worth of greens but i think it is a sacafice i must undergo. Thx for all the help you guys