I like the idea of special colors. Hell, make it so that you can color in detail...maybe color the tail feathers and tips of wings, which would give people a bigger differential in looks for different people. Yeah, Black chocobo with white tail feathers and blue wing tip feathers....almost multi colored. Or maybe some way to maybe prestige the chocobo. Once you get to highest lvl, knock it back to lvl 1 but carry over a portion of a base stat which depends on the role that you chose for your chocobo or based on percentage of total skills vs. skills in each role.