I have not personally observed this effect at all. I have only seen them take away color, not add it. I am coming up on another 6 hour period being finished, so perhaps I will be proven wrong if the chocobo comes out a color other than what is predicted.
By your own reasoning, this would make it impossible to get white, btw.
There are already verified snow white chocobos.
It is an unnecessary complication to believe that the fruits that "lighten" colors actually secretly darken others.
