Dawn made a very good point when she asked why Snickers is called a chocolate doe, because Snickers is silvery on the back and only chocolate on the face and ears (and feet, but you couldn't see those).
Angora wool, which grows on the body of the rabbit, comes in much lighter than the shorter hair on the face, ears and feet. So we go by the faces when we're talking about the colors of the rabbits. The color seems lighter on the body because of the wool. The guard hair, which is sprinkled in the wool, has a lot of the color that the face does.
So, if you have a chocolate bunny that is born looking like this:
She will grow up into a beautiful doe that looks like this:
One of my goals in raising the colored Germans is to deepen the color in the wool. My black rabbits have a black face and a gorgeous pewter wool when they mature that is my favorite angora to spin. Chocolate is lovely too; I've been spinning some chocolate angora, some angora blended with wool and silk and I have some Jacob roving. I hope to put it all together into a natural color vest someday.