here are my thoughts so far:

lets assume you are at dessert yellow and want to go to blood red
lets also assume that blood red has a R/G/B +/- color range that any R/G/B value within that range snaps to Blood Red and you feed your chocobo any variety of fruit that falls in that range and gets the Blood Red color.
I do not think that after your chocobo changes to blood red that the R/G/B color values become the perfect Blood Red values. I think that you are still sitting in the range.
Now if you want to go from Blood Red to another color and hit that one exactly on the R/G/B values. You need to know where you sit precisely for your current values and mathematically go from there using the +8/-8 formula and the new color scale i posted.

edit: continued on next page