After seeing this thread I fed my chocobo some more fruits.

I had given him 1 O'Ghomoro berry earlier today.

I just gave him another one and nothing appeared on screen so I used 2 more, after that it showed the message "It's Growing new feathers" and showed the time until the process completes. (1h 44m)

I assume that every time that the "New feathers" message appears it changes from one colour to another.

(I'll post the results as soon as the time passes.)