A calico-colored cat is a white-based cat that has large splotches of black and large splotches of orange that don't intermingle. Black, orange, and white are all (for the most part) separate.
A tortoiseshell-colored cat has black and orange mixed in together, in a brindle-type pattern. The majority have a 'split' nose....black on one side and orange on the other. They can also have white on them....but that makes them torti and white, not calico.
Some cats couldn't 'decide' which they wanted to be, lol....and end up with some calico-colored body parts, and some torti-colored body parts.
The situation is further complicated when you have torti and tabby markings (stripes) at the same time. We call that a 'torbi.'
I confuse the two.