The black (I'm assuming you probably have 'Black Magic') will fade to green in shade or part shade. They like lots of sun. Actually, the green ones (Colocasia esculenta) also like sun pretty much, but can probably tolerate less sun than the black - it won't affect their color, but they might begin to look kind of leggy. If they do, you can always move them to a sunnier location.

Are you planning on bringing them indoors during the winter or do you live in a tropical zone? The ones that are in gallon pots can probably be planted up into about a 10-12" pot. Your tubers can probably be planted about 2-3 to a 10-12" pot.

I would use a well-draining potting soil (maybe add some more perlite or bark chips to it), and feed it regularly - Colocasias like to be fed a high phosphorous or well-balanced fertlizer on a regular basis.

Susan