Dump the guy that won’t go a 2 wire pump; they are as good as a 3 wire and the motors are made by the same company.
Then use the red start wire as ground and mark it (green) accordingly everywhere it is visible. The requirement has to be they want a ground, not that they require 4 wires. Otherwise I’d let them sue me and I’d fight them.
Where is this being done?
Quality Water Associates