A field guide to mesozoic birds and other winged dinosaurs

Feather Color
Recent work by Jakob Vinther and others on reconstructing the
life coloration of prehistoric birds has been some of the most exciting paleontological
research of the decade. Prior to this research, artists were often
considered to have had total license to imagine the external appearance of
prehistoric dinosaurs. However, even without direct measurement of colors
and color patterns in fossil species, there are certain biological factors
which go into bird coloration which have been largely ignored by artists in
the past.
There are several processes that add color to feathers. At the most
basic level, these can be categorized as either structural color or pigmentation,
though often these two modes combine to create the life coloration of
a bird.
Structural colors come from the actual physical structure of the
keratin or melanin in the feather. At the microscopic level, many feathers
exhibiting structural color have a “foamy” texture of tiny spheres or channels
which enclose minute air bubbles. Light scatters through these bubbles
in various ways depending on their exact arrangement. The development
of these complex structures has recently been examined by Dufresne & al.
(2009). Alternately, the structure may be produced by the layering or physical
arrangement of melanin granules in the feather (Stettenheim, 2000).
Structural colors can have two effects on the life appearance of an
animal; they can produce colors not found among the various pigments,
and enhance or change pigment colors. For example, among amniotes (vertebrates
which lay shelled eggs), there is no known method of blue pigmentation.
Blue skin, scales and feathers are produced by light scattering due to
structural configuration. Similarly, iridescence as seen in many birds comes
from the feather structure. A bird with bright white or pitch black feathers
likely uses structural colors in addition to pigments (or lack thereof) to
achieve this effect--without them, these colors would be flatter, duller, and
less vivid. Structural coloration can also act as a filter, modifying the light
reflected by pigments to form new colors. In most birds that have them,
green feathers are produced by layering yellow pigmentation nodules over
a blue-producing underlying structure.
Though harder to find in the fossil record than pigments or chemical
traces, structural color can be found in some fossil feathers. Iridescent
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