The Anthracite mutation has an incompletely dominant relationship with its wild-type allele. That is, it shows a visible effect when present as a single factor ( SF) and a different effect when present as a double factor ( DF).

In the green series varieties the SF Anthracite Light Green has one Anthracite allele and one wild-type allele at the Anthracite locus. This darkens the body colour to a shade somewhat deeper than a Dark Green. The DF Anthracite Light Green, with two Anthracite alleles, is a deep olive colour.

In the blue series varieties the SF Anthracite Skyblue has one Anthracite allele and one wild-type allele, with a body colour rather like a deep Cobalt. The DF Anthracite Skyblue with two Anthracite alleles, the true Anthracite variety, has a dark grey, almost black, body colour with mauve overtones.

Because the Anthracite factor is always visibly expressed no budgerigar can be split for Anthracite. The heterozygotes of Anthracite with just one Anthracite allele correspond to the splits of recessive mutations.

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. In fact, the similarity of the Anthracite to the English Grey is striking. 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.

The interaction of the Anthracite and Dark budgerigar mutations has not yet been investigated. It is expected that a combination of the two factors will deepen the body colour even more