The basic pigment deposit in the feathers of a pigeon is called melanin. Pigeons only create a single kind of melanin, while many other birds produce two, or even three different kinds of melanin.
The difference in colour we see in wild type pigeons is caused by different patterns of pigment deposit in the feather. Three different types of deposit are recognised:
- Smooth Spread - This causes the colour of the tail bar and wing tips of pigeons. Because the pigment is smoothly and evenly distributed everywhere, most of the light falling on the feather is absorbed and not reflected back to us, giving a very black appearance.
- Coarse Spread - This causes the colour of the pattern area of the bird. The pigment is still distributed over the feather, but microscopic investiations showed that the pigment is not evenly spread across the feather, but rather thicker in some places and thinner in others.
- Clumped - This causes the range of blue that we see in wild pigeons. Here the pigment is clumped together in varying degrees giving the various shades of blue, from the darker (not black) head, to the light blue of the wing shield and breast.
Different mutations have caused different changes to the melanin deposits of pigeons.
For example, changes base colour are caused by mutations that change the structure of the melanin itself.
Other mutations will inhibit melanin deposits in certain areas, or enhance deposits in other areas.