Well, given that this is a zoo bird he is a little more pink than red or scarlet. Like flamingos they get the red coloring from the crustaceans they eat so zoo birds tend to be a little less brightly colored than their wild counterparts.
The color comes about because they digest the shells, the chemical that turns your lobster bright red when you cook it is the same one that accounts for the coloring of ibis and flamingos. It travels through the body and gets deposited in the feathers as they grow, so the pigmentation is not from a dye process like some might assume.
Interestingly enough there is a similar process in humans that has been fairly well documented. There are people who drink a liquid solution of colloidal silver thinking that it will help prevent infections (pro-tip, it doesn’t), too much taken over your life span will result in gray-blue skin, it is a condition called argyria and this article explains the process. People are weird.