The Black Market is an area in Sonic Adventure DX, Sonic Adventure 2, and Sonic Adventure 2 Battle. In Sonic Adventure DX this is only accessible via the Station Square Garden. In Sonic Adventure 2 and Sonic Adventure 2 Battle, this area is only accessible via the Chao Kindergarten.
Here you can buy various items for your Chao, such as fruit, seeds, and even hats with the rings you've collected in the action stages. Rarer items will only appear when you get more emblems, though! However in Sonic Adventure 2 and Sonic Adventure 2 Battle, you can buy the Omochao Voice, Amy Voice, and Maria Voice for your menu screen.
You can get different coloured Chao Eggs from the Black Market. However hatching these provides no sort of stat boost of any kind or any change in the way it is raised. Chao with different colours can still be raised like any other Chao.
Keep in mind, that even if you have the right amount of emblems, you still may not see the egg you want. This is because there are some colors of eggs you will never see on 1 save file(For example, if you never see certain eggs and have 180 emblems, chances are you won't see them). You can also buy special fruit from the Black Market. Unlike the
fruit readily available from the trees in the gardens, these can
boost other stats, as well as other things. Additionally, you can buy seeds to plant in your garden to make fruit. Finally, the Black Market also sells various objects your Chao can wear on
it's head. To enable a Chao to do this, it must have had at least
one Skeleton Dog given to it. Also, some Chao won't wear one no
matter what you try. The hats can make your Chao look very cool,
or silly, depending on what you have it wear. (Items marked with * are unobtainable)