These three patterns are very similar so it can be tough to tell them apart. Even after learning the differences, it'll take time before you can quickly identify the pattern
Let’s start with the tortoiseshell.
Tortoiseshell
The tortoiseshell pattern was named after the tortoise because of the resemblance to their shell.
It is called a bi-color pattern, meaning that it consists of two colors: red and black. Or in the case of dilution: blue and cream. Cats with a white undercoat are called, ‘tortoiseshell and white’.
Here is a picture of a tortoiseshell (tortie) cat:
Image by XXXvaldemar via Pixabay
Note how the fur has a mottled or blotched look to it; the colors almost blend together.
Calico
The calico is considered a tri-color because it always has white, unlike the tortie. They’re black, red, and white. In dilutes, they are blue, cream, and white.
Here’s a calico cat:
Image by Xtrodinary via Pixabay
As you can see in the picture above, the red and black are in big patches, differing from the tortie.
They can have from 25% to 75% white.
Patched Tabby
The patched tabby pattern is brown tabby with red and occasionally, a white undercoat.
Image by StorageJim via Pixabay
Notice the tabby base with red patches and how it almost blends in together like the tortoiseshell.
Other names used to describe this pattern are torbie (tortoiseshell and tabby) and caliby (calico and tabby.)