Is the yellow skin of a raw chicken indicating that it has been dyed? Yellow skin in raw chicken is seen is some parts of Mexico and I was wondering if that color is obtained using dyes. I've done lots of research both online and asking people who have knowledge about raising chickens but have received a lot of conflicting information.

To be clear, this is the kind of yellow I'm referring to:


So far, I have found the following things, which some contradict each other:


The yellow skin is caused by eating marigolds.
The yellow skin is caused by dipping the chicken in hot water and removing quickly.
The skin is dyed yellow due to cultural reasons.
The skin is dyed yellow to help with gutting the chicken.
The skin is dyed yellow to give it a more tasty look.
The yellow skin is caused by eating grass.
The yellow skin is caused by eating special bird feed to puff up the chicken.
The yellow skin is caused by eating carotenoids.


Does anyone have more information about what really is causing this intense yellow? I'd appreciate a paper, research or official information so I can use this to stop the spread of misinformation among my local community.
The skin is yellow probably because the chicken was fed with maize. 
Age and race of the chicken are a factor, too.

In Germany (and propably Europe) you can explicitly buy „Maishähnchen“ that is fed purely with maize. 

If you compare this with the standard grain (wheat) fed chicken you can see the distinctive difference in Color