How to create an on/off indicator for a SPST in a circuit?
This circuit will work regardless of the type of SPST switch



With the switch closed a current will pass through LED1 and R1 and turn the green LED ON indicating the switch is closed. R1 is chosen to limit the current through the green LED. In this case 1k0 will limit the current to about 7mA ((9 - 2)/1000).

This will also produce a voltage drop of about 2V across the green LED. R3 and R2 divide this voltage drop so that at Q1 the base - emitter voltage will be less than 0.6V (= 0.35V). The transistor Q1 will be turned OFF. If you find the transistor is not turned off you can always lower the value of R2. 

As Q1 is OFF no current can flow through Q1 and the red LED will be OFF.

When the switch is OPEN no current can flow through the green LED so it is OFF. The base of Q1 is now connected through R1 to ground. The voltage at the base of Q1 is sufficient to turn the transistor ON (0.6V). Current now flows through the transistor Q1, R4 and the red LED which now lights up indicating the switch is open.