Um, I've never bred a chocobo from two coloured parents and not had it turn out the same colour. If you want a red choco breed two red chocos together. I've never heard/read anything about feed changing the chances of different colours.
HOWEVER. Choco raising needs to be improved/simplified. I'd like it to become WORTH doing even slightly by making it so that a raised choco CANNOT be slower than a rented one, but they can be faster (so the opposite of now, where you need to breed/raise a choco perfectly to get it the SAME speed as a rental). I love pulling out my blue choco but it sucks that I need to rent when I'm riding with friends because he can't keep up. Also choco items for GIL on NPCs please. Chocobucks are not a useful currency.