The gene that is less dominant than the "full-color" C gene is the chinchilla gene [c(chd)]. This gene is what turns a chestnut into a chinchilla or an otter into a silver marten, an opal into a squirrel. what it does is to remove the "yellow" color of the chestnut, otters and opals. This is also responsible for turning a "golden-tipped" steel into a "silver-tipped" steel. A gold-tipped steel has the full color gene [C] and when the gold or yellow is removed you get a white-tipped steel with the [c(chd)] gene (More about the steel gene later).
Rabbits that have the [c(chd)] gene instead of the full color [C] gene is the chinchilla, squirrel, and all silver martens.
Chinchillas and squirrels are "agouti", "black", "chin" rabbits and the genetic code for them is:
If a "self" rabbit [a][a] inherits the chin gene instead of the full color gene, you have what appears to be a "self" colored black, blue, chocolate or lilac, and about the only way to tell the difference between a true "self" rabbit and a "self chin" is by the pedigree, and also in the offspring...as the rabbit appears to be a "full color" rabbit, he will produce like the chin that he is! I have noticed that as young bunnies--"self chins" often have a lighter color on the underside of the tail...even appearing to have a nearly white underside of the tail at times. They usually outgrow this and it is only important if in your breedings, you want or don't want the chin. I also expect that the color of a "self chin" would not be nearly as good as it's "full-color" competition. If you are working with "pure lines"--that is rabbits that have all 1 color on a pedigree...it is possible to get a "self chin" from breeding 2 "full color" self rabbits...example--2 self blacks...could produce a "self chin"...One of those "full color self" parents donated the chin [c(chd)] gene and the other donated a gene that is recessive to the chin gene, that could be the shaded [c(chl)], the himalayan gene [c(h)] or the REW gene [c]. I suspect that some of the people working with pure lines of self rabbits and suddenly have an off-color "self" rabbit, have actually gotten a "self chin".
Also, you can be sure that if you have a "self" colored rabbit on a pedigree (black, blue, chocolate or lilac) and both parents are "chins"--that is either chin, squirrel or silver martens..that bunny is a "self" chin and NOT a "full colored" "self" rabbit. As in order for the bunny to become a "full colored" self...he would've had to inherit the [C] gene, which is more dominant that the chin gene. And in order for a rabbit to have a more dominant gene...it has to have at least 1 parent that has that gene to pass on to the offspring.