Control two LEDs with two wires and inverter
When using a red and green LED, you can utilize the difference in LED forward voltage as in the circuit below. Make sure to use high efficiency LED's. These have a low internal resistance and a nice and sharp bend in the forward voltage/current curve.







simulate this circuit &ndash; Schematic created using CircuitLab

Normally the green LED lights, which has a forward voltage of approximately 2V. Then when the switch closes, the red LED light and due to its lower forward voltage, approx. 1.8V, the green LED will turn off from (voltage) starvation.

If the green LED does not entirely turn off, you can add a regular 1N4148 diode in series with it to make the effect stronger, but this is usually only necessary with cheap and relatively low efficiency LED's.