Is there a standard for wire color for the 12 house system? ...
In the US, there is no standard color scheme for low voltage (below 30 volts, nominal) wiring in a vehicle.
For battery cables, Red is usually positive and Black is usually negative, but for individual circuits it is all over the map.
I prefer the DIN/TUV standard for low voltage ground, which is light brown. While there is nothing wrong with black, as has already been noted, it is used for hot on the high voltage side, and choosing a different ground color can avoid confusion. For the same reason, green would be an acceptable choice for ground wires, but many vehicle manufacturers use green as a hot lead for many circuits.
In the boat world, there is actually a standard and it is set specifically to avoid confusion with high voltage circuits, which, on boats, are often run in the same chases and panels. When a high-voltage system is present with black hot wires, then Yellow is the preferred choice for low voltage ground return leads.
... AC voltage must be lightest color for common but not white if a green is present. Remember white is not a color.
This is just plain incorrect and is dangerous advice. Neutral wires, confusingly known in the code as the "grounded" conductor, must
be WHITE in all cases. The code makes no exceptions here, although wires over a certain diameter may be marked with white tape at the ends rather than continuously white. For everything we would use in a bus, they must be covered with continuous white insulation.
On molded appliance cord (as opposed to built-in wiring), also known as "zip cord," BTW, the grounded (neutral) wire must always be specially marked; most manufacturers mold a rib or ribs into the neutral for this purpose.
Safety ground, known in the code as the "grounding" conductor, MUST be either bare copper, green, or green with yellow stripe. Again, no exceptions until you get into very large diameters, where again end-marking with green tape is permitted.
Technically, by the way, white is
a color, or, more precisely, a range of colors which, for transmitted light, is characterized by a parameter known as "color temperature." It can be argued that pure black, however, is not a color.
For the purposes of wiring standards and codes, both black and white are called colors.