There are two colours known by the hobby name of Chocolate.
Sex linked recessive Chocolate is only found in Orpingtons & Wyandottes in the UK, and in Seramas.
Being sex linked recessive a hen only has one gene, i.e. choc/- and is Chocolate, males need two i.e. choc/choc to be Chocolate, heterozygous males i.e. choc/Choc+ are Black.
The Chocolate found in Polish(Poland),OEG & Dutch bantams is heterozygous Dun, an allele of Dominant White.
Birds,both sexes, that are heterozygous i.e. I^D/i+ are the darker shades of brown ,Chocolate. Homozygous birds I^D/I^D are shades ranging from a pale brown ,Khaki to a Dun Splash. The inheritance of Dun is the same as that of Blue,Bl.
David