The B_ gene set.

Gene set B_

 The B_ gene set controls weather the base color is brown or black.

The Black gene.

 The black gene (B_). The black gene means black is the base color of the bunny's fur coat, that means that any color that is black changed black like blue (looks dark grey colored) has the base black colored gene.

Variations of this gene: B_ & Bb.

The Brown gene.

  The brown gene (bb). The brown gene means chocolate is the base color of the bunny's fur coat, that means that any color that is chocolate or lighter or somewhat changed brown colored such as orange has the base chocolate (brown) colored gene.

The only variation of this gene to show is bb.

Here's some punnet squares for the variations these genes could have as out comes. 

Here is if parent 1 with BB genes had offspring with parent 2 who had bb genes, all offspring would be Bb (black colored and carry the recessive b gene).

 

Here is if parent 1 with Bb genes had offspring with parent 2 who had Bb genes, 50% would have Bb genes (black colored and carry the recessive b gene) and 25% would be BB (full black gene) and 25% would be bb (full brown gene).

 

 Here is if parent 1 with Bb genes had offspring with parent 2 who had bb genes, 50% would have Bb genes (black colored and carry the recessive b gene) and 50% would be bb (full brown gene).