I have only been using apples so far. Nothing else. It has gone as such (if anyone else is doing apples only and sharing progress every time the feathers change message appears...):

First bunch of apples before I tried started to experiment more precisely: Pumpkin Orange.
Second bunch of apples until I got feathers changing ONCE then waited six hours: Sunset Orange.
Gave him a bunch of more apples until I got feathers changing ONCE, and am waiting for further results. I'm hoping the trend continues to strengthen red and it will be one of the -red- reds, Blood Red etc. Will post.

Others who only use apples could try and see if they also get the same results from Pumpkin -> Sunset with one feathers changing.