ungrounded conductor

The code does not allow what the GC is asking you to do. The grounded circuit conductor should have white insulation. I would not pay until it is corrected. You will not find a code article to allow re-identification for #12 awg conductors. Article 200.6(a) and (b) of the 2008 NEC will explain this. The white conductor is a grounded circuit conductor.

Somewhat OT, Bah, but I've long wondered and not too successfully Googled the q, but officially what are white, black red, and green supposed to be used for respectively

The NEC does not specify colors for phase conductors like it once did. In a residence or where NMB Romex is used a two conductor cable with have Blk (Hot) White (grounded circuit conductor) and bare (equipment ground). Where a three conductor NMB Romex is used you will have Blk and Red (Hot Conductors) White (Neutral conductor when 120/240V circuit or Grounded circuit conductor when Blk and Red are used as travelers on the 3-way switch circuit as an example) Bare or Green (Equipment grounding conductor). In commerical installations if the system is 120/2083ph4w Y phase-A: Blk, Phase B: Red, Phase C: Blue and the Neutral is White. For conductors larger than #6 tape is used to identify the conductors at termination points otherwise the conductor insulation will be black. For a 277/480 3ph4w Y system the phase conductors are identified A-phase: Brown, B-phase: Orange, C-phase: Yellow and Neutral white. The colors are what is used by the industry as a standard but not required by the NEC with the exception of The High-Leg of a 120/240 3ph4w Delta sytem which is required to be Orange. The colors required for the Neutral, Grounded Circuit Conductdor and Equipment Grounding Conductor are code specified.

Thank you Bah, I've saved that for future reference

Seems to me there ought to be more colors, more standardization