Paul,
Actually this change was made in the 2002 code. Prior to that the code used the words "natural gray". This is an old term from the early years of thermoplastic insulations and was a "natural" color, that is colorants were not added when the insulating material was made. "Natural gray" has not been available for 30 to 40 years. The use of wire with a gray insulation as a grounded conductor prior to the '02 code was actually a code violation, even though it was also a very common practice. There have been atempts to make this code change in 3 or 4 code cycles prior to the '02 but they were not accepted. All of these proposals cited the common practice of using the manufactured color gray in place of the required "natural gray", but it wasn't until the '02 that a proposal was accepted. The fine print note was added because, even though it was common practice to use the manufactured color gray for the grounded conductor, this color was permitted to be used as a hot conductor. Just another reason why we should never rely on wire colors to determine the voltage and function of a conductor.
Don
