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I will assume it is true that the allele causing a ash-red plumage is dominant over all other alleles. Note however that you should cite your reference when making such claim in your post.
Dominance and allele frequency
Phenotypes associated to a dominant allele
A aren't necessarily more common than the phenotype of the recessive allele
a. It all depends on the allele frequency. If the dominant allele is at low frequency then both
Aa (both displaying the dominant phenotype) are at low frequency (esp.
AA individuals) and most individuals are
aa and show the recessive phenotype.
You might want to read about Hardy-Weinberg rule with this post for example.