Just read the 2005 code mentioned by Don, and it seems it is very simularly worded to the 200.6 code section that is specific to grounded conductors, but adds system identification for phase conductors as well. (I guess just short of going as far to have color codes involved in the NEC.)
https://www.electrical-contractor.net/ubb/Forum19/HTML/000061.html

Mark Heller
"Well - I oughta....." -Jackie Gleason