The term "proper" is used when a charge is emblazoned in a manner as it appears in nature and is considered heraldic shorthand. Thus, instead of saying A pine tree vert, trunked brun, one blazons it A pine tree proper.
Following is an alphabetical list of proper tinctures for various birds. Links are provided either to the LoaR/cover letter with the decision, or to the Glossary of Terms table on Proper Tinctures.
Flamingo
"In April 1985 (q.v., Cherie Ruadh MhicRath of Locksley) Laurel ruled, "The color of a flamingo's feathers is apparently dependent on its diet, so there really is no 'proper' color." This has been interpreted to mean that flamingos proper could not be registered; however, pink flamingos proper have been registered since that time, including as recently as April 2006. The 1985 precedent is hereby overturned; a pink flamingo proper is registrable. (sic) It is dark pink while the tincture of its beak and legs are treated as artistic license. Its tincture is a color, not a metal." (Marion Baggeputz, 02/2007, R-Calontir)