Colours in art packages are often given hex codes as illustrated below with #00ccff. why is hex used in this way rather than the actual 24-bit colour value?

There is no technical reason for using one or the other, a computer could easily handle both variants.
The reason for hex is that it is so much more intuitive and practical to use. It is quicker to write, because it requires fewer characters. With bits, you would be very likely to miss count at some point and also wouldn't notice typos, because who actually remembers all 24 characters. The length also makes it harder to read: where does the green channel start/where is the 9th character?
Additionally, hex numbers are closer to the typical decimal system, only adding 6 symbols, while with binary you remove 8 symbols, which makes it a bit more familiar and easier to learn.

Hdi4nfnfuhdjdurjfjc7fjrnckf snuck fhfjfkfmfjfk4jrhr