The B locus is the most basic color locus. It controls whether the rabbit has a black or chocolate base color. A rabbit can be either B_ or bb.

B_ is black-based. Black can be either BB or Bb. It is the most dominant on the B locus. Varieties recognized in Holland Lops that are B_ at the B locus are:
~Black
~Blue
~Chinchilla
~Squirrel
~Chestnut Agouti
~Opal
~Black/Blue Pointed White
​~Black/Blue GT/ST Steel
~Black/Blue Otter
​~Orange
​~Frosty
​~Red
~Cream
​~Black/Blue Tricolor
~All Shaded varieties except for Chocolate Tortoise and Lilac Tortoise

​bb is chocolate. Chocolate can ONLY be bb. Chocolate is recessive to black. Varieties recognized in Holland Lops that are bb at the B locus are:
~Chocolate
~Lilac
~Chocolate Agouti
​~Chocolate Chinchilla
~Lynx
​~Chocolate/Lilac Pointed White
​~Chocolate/Lilac GT/ST Steel
~Chocolate/Lilac Otter
​~Chocolate/Lilac Tricolor
​~Chocolate/Lilac Tortoise