[1] A single Anthracite factor has a similar effect to the Dark mutation, causing a Skyblue to become Cobalt in appearance.
The Anthracite mutation appeared in Germany in 1998 in the aviaries of Hans-Jürgen H Lenk, who successfully established the strain[2] and continues to report on its development.
[3] Initially found only in Germany, by the end of 2008 descendants of this original mutation had been exported to America, Belgium, Canada, England, Finland, Holland, Italy, Norway, Sweden, Switzerland and Pakistan.
A single Anthracite factor has a similar effect to the Dark mutation, causing a Skyblue to become Cobalt in appearance - as was suspected with the English Grey.
The description is virtually identical, and the cobalt appearance of a Skyblue with a single Anthracite factor is exactly what was suspected for the English Grey.