How would one create that sort of chocolate brown patina? I like to make
copper and brass tokens for my shop and would like to give them a nice
dark
brown, deep green or blue patina.

The brown forms naturally in air. Keeping the coins hot and in supply
of oxygen would speed this up. Naturally formed patina is better and
more durable than any chemical cheat, and you can have good results in
a few weeks. Worth trying if you are patient.

Patination quick solutions:

Ferric nitrate will turn copper brown to orange, Liver of Sulfur will
promote formation of the black oxide, and Copper nitrate will give you
a green patina. I believe the green is usually lacquered over for
durability. I've never tried any of these; my polished copper items
turn brown so fast on their own I've never looked into speeding it up
:-)

I would not think it desirable to have sulfate or carbonate formation
on your coins (shades of green and blue you see on outdoor copper
items, especially by the ocean), because these can rub off and are
toxic.

-Adam