Controling 3 LEDs using only 2 IOs
If both IO lines have the same logic level then neither of the two LEDs would light so you use this to control a 3rd LED but I think you need two diodes acting as a sort of AND gate: -







simulate this circuit &ndash; Schematic created using CircuitLab

If either GPIO line is low then the LED won't light. If both GPIO line is high then the LED lights.