Three articles for you. The first two are about a study that managed to isolate the gene that allows parrots [they did it with budgies] to go from green to blue and now, back to green!!!! SUPER interesting and I'll give you the highlights to whet your curiosity:
1. Both blue and green budgies have the yellow pigment gene
2. The pigment is 'carried' to the feathers in an enzyme
3. This enzyme has one single substitution of an amino acid which prevents the blue budgies feathers from 'acquiring' the yellow pigment
4. This enzyme dies BEFORE the feather is mature!
The third one is about the red color in birds but take into consideration that parrots produce red in a different way of all other birds.
https://phys.org/news/2017-10-yellow-bl ... rrots.html
http://med.stanford.edu/news/all-news/2 ... olors.html
https://phys.org/news/2016-05-genes-ena ... s-red.html