Explanation of the terms: Isabella, tawny and light fawn shades:
Bergamascos are only able to produce eumelanin pigments (black without any tan on the dog).
They do not produce any phaeomelanin (which is predominantly tan, and responsible for red/yellow pigments). Therefore the breed cannot be brown, tawny, sable or any color in that family.
The word "shades" used in the standard is not a real color. What the standard really means is that under the influence of sun and water and atmospheric factors in general as well as ageing of the hair, the loose hairs, which form part of the map mass, gradually change color: the grey hairs turn yellowish while the black ones take on a tawny hue. This is what causes the Isabella and light fawn shades visible in the coats of adult dogs. If the maps are lifted up and the hair examined at its roots, close to the skin, the coat is either grey or black.
It is unfortunately the case the recent appearance on the scene of Bergamascos with tawny-black coats or sable colored coats. Since these coloring are not mentioned in the standard, their presence is undoubtedly due to spurious introduction of crossing with breeds in which these alleles are present (German shepherds, Briards). Careful checking of adult dogs and, above all, detailed examination of puppies is essential in order to preserve the integrity of the breed.
Note that the Isabella colors is not accepted in the standard, nor is a Tawny (Brown) Coloring