Chris Green wrote:

Is there any sort of standard though?

Not really, spax use colours for size, wera use it to distinguish
slotted/pozi/torx/hex/etc

https://www-de.wera.de/fileadmin/images/greattools/gt-take-it-easy-1.jpg

https://wickes.scene7.com/is/image/travisperkins/GPID_1100579732_00?id=1OvRV2&fmt=jpg