Chinchillas are much easier than other animals to figure genes on. Most colors they either have them of they don't and you can tell by looking at them. The only colors that can be carried and not seen are Violet, Sapphire, and Ebony. Every other color is dominate so it will show on the coat, ears, or eyes if the chinchilla carries the gene.
Your chinchillas are ebony. People used to call them homo ebony for solid black and hetero ebony for darker grey. We now know that ebony is a wildcard gene that doesn't follow that rule. After 15 years of breeding I have learned it seems to have no rules! It can come from only one parent and show solid black, it can come from both parents and be dark grey, it can hide in a white bellied baby and she can go on to produce a dark bellied baby. Its a crazy gene.