How to create a simple wiring diagram with 2 voltage measurement LEDs?

Question

Electronics

I want to put a voltage indicator in the car instead of the alarm LED. Those. if the supply voltage is below 11 volts, then the red LED is on, and if it is higher, the green LED is on. The LED still blinks, then let it show the voltage at the same time.
If you can something simple of 2 diodes, 1 transistor and resistor.
And if possible an option for 3 LEDs.
The main task is to make the LEDs burn only in turn. I don't want them to light 1 or 2 LEDs. Only in turn.

Answer 1

Up to 11V red, above 11V green. Yellow above 15 V The
yellow LED with all its wiring can be thrown away.

Answer 2

Can be done on a 555 microcircuit (plus one diode and several resistors). https://www.homemade-circuits.com/simple-low-batte...
Connect the second LED between + power and pin 3 (through a resistor, of course).