Is Black Chestnut a variation of chestnut? Or is it the result of certain color genes working together?

Just a variation of chestnut I believe

Technically a chestnut variation, but requires a certain agouti gene.

There's a lot of debate about this, as the game guide and the news page say different things if I recall correctly, but through my own research, looking at gene tested black chestnuts born after the gene update, I've come to the conclusion it needs to be Aa, aa, or Ata to be a black chestnut. AA, AAt, AtAt, etc, don't work.

Thanks!! The two I have (unrelated) are both aa. I couldn't find those earlier discussions to check.