I don't know how a judge reads it, but I'm wondering if "some chestnut permissible" has the implication that a little chestnut is tolerable though not desirable. In other words, with two otherwise identical roosters, would the one with "some chestnut" be judged lower than one without any chestnut?
Or maybe I'm reading way, way too much into this.
Yes, this is how it is described by the UK show winners. But in most birds of the same caliber in body shape, it is the rooster with smudges of chestnut that wins over the bird with red in the shoulder. Double barring and cream can dilute mahogany, but not red.