Grounding conductor has a non-zero voltage (i.e. with respect to "true" ground). Why?
One possibility is that your power supply is not single phase as you state, but rather split-phase.

If that is the case, you don't have a hot and a neutral, but two hot wires. The two hot wires are 120V to ground each, and 180° out of phase, resulting in 240V across them.

This would explain your 240V line voltage, your 120V hot-earth and "neutral"-earth measurements, and the identical wire colors for your hot and "neutral" wires.

To confirm or deny this, you could (carefully!) measure the voltage between your hot or "neutral" and a known ground reference such as a stake in moist soil, or a tap water pipe - assuming you have metal piping.