This species (group) of Amazons are best defined by their clear /yellow of their bill and nails! The four species that have that clear/yellow are found fairly close to each other geographically. It is important to know that when there are light to heavy darker areas, that implies an additional species within the group. They commonly do not interbred and as a result hybrids are not common. That said, it is not uncommon for them to push base colors anywhere on their body and from time to time on their wings and tail feathers.
I am going to guess that you did not receive a Hatch Certificate with your Amazon, correct? All Amazons under the age of 5/6 must have a Hatch Certificate that states, separately, the species of each parent, the hatch date, the name and contact information of the Breeder, etc. Plus, each transfer point between that and you.
Let's talk about his coloration and dispel some theories regarding them as near all parrots can as a result of their DNA, Diet and Health, result in the eruptions of color in fields not normal found. Examples: Yellow and/or Red on the Back or Breast. Yellow, Red or both on the crest/top of the head. As a result, it is critical to first determine the overall health of the Amazon and with that begin to define .
While at the upcoming vet visit, please have the Avian Vet begin to reduct the length of his upper bill.