Astaxanthin is responsible for the pink plumage flushin Franklin’s and Ring-billed gulls

Carotenoid pigments produce the red, orange, and yellow plumage of many birds. Carotenoidcontainingfeathers are typically rich in color and displayed by all adult members of the species. In many gulls andterns, however, an unusual light pink coloring (or flush) to the normally white plumage can be found in highlyvariable proportions within and across populations.

Kevin J. McGraw and Lisa S. Hardy, J. Field Ornithol. 77(1):29-33, 2006