Per the 310.12, as previously noted above,
it appears that the NEC should mandate a color for a covered or insulated GEC.
310.12(A) Grounded Conductor ID, (200.6).
eliminates White or Gray.
310.12(B) Equipment Grounding Conductor (EGC) ID (250.119).
310.12(C) Ungrounded Conductor(s) ID (last 12 words of 1st sentence).
This Section does not leave many common colors to be used for the coverd or insulated GEC.
I certainly do not know why Green should not be used. The GEC is for grounding.
If some other color than Green were to be used for a premise GEC, then a Sign would need to be prominate on eacb panelboard through-out the premise to abide by 210.4(D) to include the GEC color is not to be used as an ungrounded conductor.
