Small letters be used in IPv6 addresses

I have notice that it has become a norm in the industry NOT to use capital letters when dealing with ABCDEF characters in IPv6 addresses either in documentation or in actual DNS entries. For instances:

2001:371::ABCD should be avoided and
2001:371::abcd should be preferred.

Actually, the use of small alphabets will cause more reading errors such as a, b, c and d all confusing with 0. On the other hand, capital letters tend to cause less reading errors (just B and D confusing with 8 and 0). However, small letters are chosen because the majority of named servers are operated under Linux and Unix OS which are case sensitive and traditionally small letters are used in these OS.