True, however as you are no doubt aware, one more digit or one less would double / half the karma requirement which is somewhat extreme, and it would no longer be representable by two hex digits.

The CSS colours are specifically 3 octets written as 2 digit hex, so you so while I like the broader idea that "it's a byte of karma" is sufficient, knowledge of 2 digit hex codes also applies to the privilege directly.

Plus, non-standard byte lengths would be a much more niche reference, and I don't think people would get it.