I was hesitant to use any of the crazy sounding recipes to get blood red so I started just feeding my choco Xel Apples (darken red), these were my results (posted as a running total through the different feeding);
-4x Xel Apples : Milicorn Yellow
-10 Xel Apples : Sunset Orange
-18 Xel Apples : Mesa Red
-30 Xel Apples : Blood red
So somewhere between feeding him 18 (total) and 30 (total) darken red he turned Blood Red, all subsequent attempts to change his color past this have resulted in no "Growing new feathers" messages, I've tried feeding him more apples and nothing, I tried feeding him 5 Valfruit at once and no message, I also tried feeding him 5 berries in one feeding and once again...no message >.<
(Also, in regards to the popular color chart people are using to dye their chocos, my friend followed the Dalamud Red recipe,the exact amounts listed and in the order it is posted, and ended up with a Raisin Brown chocobo so yea...proceed with caution)