We have previously established that penciling and tarheels are not exclusive to sables that carry black. As example, Galant z Pohranicni straze and Zidane v h Sevens have those markings, but are not black carriers.
Could be that bicolor is just a less dominant degraded strain of the tanpoint allele, just as tanpoint (black/tan) alleles are just a mutated and less dominant variation of the wild type (sable) alleles. The basic principle that; "All agouti variants are due to mutated sable alleles" also allows the presence of "patterned sables" to be less confounding. Therefore, I find the notion that there could exist a precisely defined bicolor phenotype to be a pointless affair, considering that the genotype involved is a matter of fuzzy difference. Basically, the most degraded functional allele holds the least dominance in phenotypic expression.
Family strains of similar patterns sometimes have very distinct differences from those of other families. REMEMBER: alleles are not atomic elements, and should not be expected to be uniformly identical to one another. The dark sable Anrebri dogs are very distinct from the dark sable Haus Iris dogs. Black dorsal and ventral stripes of sables are controlled from the agouti locus, yet some have black ventral stripes, and some do not. Some saddles extent more than others, some blankets extend more than others. Molly's bicolors differ from other near variations, so she exempts them from her definition of "true bicolor". I'd say, give her the exclusive, and just put it to rest.
Melanism IS a legitimate term used in Molecular Genetics. Recessive variants of agouti cause melanism, which is also induced by dominant mutations in MC1R.