How many colors can you really have?

Lots of digital drawing devices and televisions will brag about how they can show billions of colors. For example, XPpen says their Artist Pro 27 device can display over a billion colors. But Color pickers in art programs seem to be rather limited in comparison.

For example, in Clip Studio paint, The color wheel has 360 degrees of Hue, and Saturation and Value go from 0 to 100. So that's 3.6 million colors. And a lot of those will just look like black. if you use Hexadecimal values, the maximum number of combinations of numbers is around 16.7 million, with 6 digits.

Is this just a big scam? can the human eye even tell the difference with that many colors?