There has to be some sort of genetic basis for the golden liver color. The dogs definitely have the recessive brown skinned genotype b/b, but I think there is another factor that makes the golden liver color. I don’t think it can be blamed upon environmental factors, and all Sussex spaniels, at least that are being bred now, are this color.
Rawdon Lee thought that the existence of “sandy” (golden) colored puppies in the early litters had something to do with it and that all Sussex were all carrying the e/e genotype. However, I have never heard of a sandy colored Sussex being born today. If they were carrying this genotype, at least 1/4 of all Sussex spaniels would be gold in color, and 1/4 would be dark livers. This is clearly not the case.
I think there is another gene that modifies the liver. It may exist in other breeds, but it is just passed off as a shade of liver or chocolate or bronze or red. (This color has many names). Because Sussex are the only breed in which this is the only color allowed and because it fits under a shade of liver, I don’t think it has been studied all that closely.
I am not sure if any of this is relevant:
http://homepage.usask.ca/~schmutz/dogbrown.html
I have a cold and I think my head my actually explode.
It may be that Sussex have a modifying factor that makes a slightly different tone to the coat color. Still, they are all bb (which ever of the 3 versions of b, Dr Schmutz does not say). The same tone of brown can occur in Newfoundlands, where it is called ‘bronze’– a much better descriptor than ‘golden’, as it is very reminiscent of the patina of old bronze.
Green is the natural color of weathered bronze, I do not think we’re talking about that, or the “chemically enhanced” patina finishes mechanically applied to bronze sculputres these can vary with shades of reds & browns.