First off, there are two messages: "Plumage will change in 6 hours!" And "X is growing new feathers!" Only the second one will mean the color changes.

Second off, each fruit manually changes your chocobo's RGB values by +5 or -5. Raptor Blue starts at 91R, 127G, 192B. Your fruit combination would change your RGB values by -50R, -10G, +80B, resulting in a final RGB value of 41R, 117G, 272B. The problem with this? You overloaded your blue value, since its maximum is 255. That's why it failed.

There is a website called www.ffxivchocobo.com that can give you an exact recipe to get the color you want. It is definitely the easiest way to get what you want.