Green phase is not confusing enough for the Swiss. HV distribution colors in Switzerland once were red, green and blue. Switched 220V phases were green too. And 15kV distribution stuff in Germany/Austria used to have yellow purple and green.
Why not a purple ground?
You could have yellow, yellow-green and green as phase colors. In fact such a combination could be seen in Switzerland, but it's confusing enough. (A light fixture could have green switched phase, yellow neutral and green-yellow ground).
The Russians had black grounds and the French had white ones.
