Both the Chinese Silkie and Ayam Cemani have been bred for thousands of years for their black skin/meat/face, recent genetic studies have confirm that they share the same mutation and give it a date of around 9000 years ago(well before the chicken domestication event)
Reference:
The origin and evolution of fibromelanosis in domesticated chickens: Genomic comparison of Indonesian Cemani and Chinese Silkie breeds.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173147
Fibromelanotic is an autosomal incomplete dominant mutation of the fm allele(Fm is the mutation and fm+ is the recessive wildtype counterpart), but here is the catch, for Fibromelanotic to be expressed at all it needs the help of the recessive sex linked dermal enhancer id+, This means that if you don't know this and you are performing a test cross of your Cemani stock with the wrong type of chicken your results will be inaccurate and may lead to the culling of a perfectly fine line.
Here is an example:
Ayam Cemani hen genetic make up:
E/E: Extended Black, black chick down
Fm/FM: Fibromelanotic
id+/- : Recessive Sex linked Dermal enhancer
W+/W+: Black Skin
Rhode Island Red rooster genetic make up:
eWh/eWh: Wheaten
fm+/fm+: non-fibromelanotic wildtype
Id/Id : Sex linked Dominant Dermal Inhibito(will inhibit any and all dermal melanin expression)
w/w: Recessive yellow skin
The result of such cross will yield F1s with White Skin, red combs and white undersole with dark shanks(Extended black allows for epidermal melanin to express)
E/eWh: Black Chick down
Fm/fm+: Heterozygous Fibromelanotic
Id/- for females and Id/id+ males
W+/w: White skin
So going by this cross you would be baffled to see that 100% of the chicks that hatched have white clear skin?
Now do the reciprocal cross(Cemani Roo over RIR hen) and you will get Sex links(pullets will hatch with black skin and cockerels will hatch with white clear skin)
Ayam Cemani Rooster genetic make up:
E/E: Extended Black, black chick down
Fm/FM: Fibromelanotic
id+/id+ : Recessive Sex linked Dermal enhancer
W+/W+: White Skin
Rhode Island Red hen genetic make up:
eWh/eWh: Wheaten
fm+/fm+: non-fibromelanotic wildtype
Id/- : Sex linked Dominant Dermal Inhibito(will inhibit any and all dermal melanin expression)
w/w: Recessive yellow skin
E/eWh: Black Chick down
Fm/fm+: Heterozygous Fibromelanotic
id+/- for females and Id/id+ males
W+/w: White Skin for males and Black Skin for females.
So even if you had pure Ayam Cemani(homozygous for the Fibromelanotic mutation) if you test it with the wrong type of hens or roosters your result will be inaccurate and I just believe that is unacceptable for someone not to mention that when writing about that on that page.
So what are acceptable breeds? Breeds with slate or willow shanks, don't use extended black birds(solid black birds) as they may have slate colored shanks but that is due to epidermal melanin and they may very well be sex linked Id.