The pigments in rabbit colors are forms of melanin. There are two main pigment producing cells. The dark colors are produced by eumelanin. This includes black, chocolate, lilac, or blue. The yellow shades are produced by pheomelanin. Orange is a name for the yellow shade. Depending on the breed, it could also be called 'fawn'. There are chemical switches that switch either the dark or yellow pigments on.
There are two ways for orange to show up in a rabbit's coat. This is where the E extension gene comes in. There are five options (called alleles) on this gene, in a series of reducing dominance. The most dominant is also very rare, dominant black E(D). So, we'll skip that. Next down is steel E(S), and then the normal color extension E that covers most of the 'normal' colors like castor agouti, black and chocolate self, tortoiseshell, etc. Castor and the other agouti colors have more than one color on the individual hairshaft, First, the dark eumelanin is turned on, and it appears at the tip. Then the dark is turned off while the yellow gets turned on, and the middle band is yellow/orange. Then it changes back again.
The last two alleles are the ones that include the orange shades. Harlequin/tricolor is coded e(j), because the color pattern was originally called 'Japanese'. It takes the banding of the agouti and instead puts the dark and yellow on separate patches of skin instead of bands on a single hairshaft. There are other modifying genes that affects how the colors are patterned, but that's another story, and not one well understood. A tricolor is just a broken harlequin, which breaks up the color pattern with patches of white.
The last and most recessive allele is a double copy of ee. It's called 'non-extension', and it turns on the yellow. In a non-agouti rabbit, the body will be yellow/orange, while the cooler points will still show the dark color. In an agouti rabbit, even the points will be orange.
Where you see variation is when other genes are involved. The D gene gives the normal 'dense' color when dominant, but the recessive version, called 'dilute', will reduce the intensity of the color. Breeds that call the normal yellow shade 'fawn', call the reduced color 'cream'. Breeds that call the normal color 'orange' call the reduced color 'fawn'. A bit confusing, but once you learn the terms for your breed, it's not an issue. On the other side, there is a reddish modifier called rufus. It darkens the shade, imagine the difference between a golden retriever orange and an Irish setter red. Rufus is not an on-or-off modifier, but rather a series of additive pluses. So you can have a little bit of a red tint or a deep New Zealand red shade.
The other place you see variation is in the self non-agouti tortoiseshell colors. While the body color has the yellow/orange pheomelanin, the points still show the dark colors. Those dark colors shade into the fawn, and tint it. And the dilute of lilac and blue tortoiseshell will reduce the orange to a straw colored beige.
So, that's why there is so much variation in the orange shades. After saying all that, I think your rabbit is definitely a black/orange. Looks like the orange has a bit of the rufus reddening, but it's lovely.
