According to the American Rabbit Breeders Association (ARBA) and their Standard of Perfection (SOP), Holland Lops are divided into the following 8 color groups:
Agouti, Wide Band, Self, Shaded. Tan Pattern, Ticked, Pointed White, Broken

 

Within each group is a collection of similar genotypes (genetic code), but the phenotypes (observable features, such as color) can appear to vary widely.  In an effort to make it a bit easier to understand, know that every bunny color is either BLACK (B), BLUE (B_ dd), CHOCOLATE (bb), or LILAC based (bb dd).  Blue is the diluted form of black, and lilac is the diluted form of chocolate.  Diluted colors as well as chocolate are more difficult to achieve than black varieties since these are recessive traits (a recessive gene has to come from each parent in order to be visible, so the mom and the dad would have to give the baby a dilute "d" gene to make it "dd" and/or a chocolate "b" gene to make it "bb" and appear chocolate).  Take a look at the following pics listing SOME of the colors within each of the 8 Holland Lop groups and whether they are black/blue/chocolate/lilac based.

 

             Tort

Tort comes in different shades from dark to light. Pictured here is a black tort, the colors of the points dictates what color tort.  Colors are black, chocolate, blue and lilac.

                           OPAL

Opal is one of my fav colors with shades and hues of multiple colors.  

                    OTTER

Jigsaw is a good example of a black otter, Blue is also an otter color and we are excited to welcome that variety soon!

Note the white inside the ear, this indicates the otter gene

, this little one is a broken black otter

                 Sable point

                                      SEAL

Here we have 2 seal, 2 black and one black otter.  Seal is a color is to be a rich, dark sepia (almost black) saddle, shading to a slightly paler flanks, chest, and belly. Color is to go well down the hair shaft, with under color to match shadings throughout. Saddle color is to extend from the nape of the neck to the tail. Eyes - Brown.

As newborn kits, the blacks look ink colored, almost dark slate and will develop into the dark black color within a few days, the seal look very close but as they develop obtain a slightly chocolate looking shimmer.

This can be noticed in some of the pictures above.