As Wali was perhaps going to suggest, this can also be done with just the 2 resistors (to guarantee the floating output is at 2.5 volts when no battery is present) and an analog input pin on the processor to detect one of the three states by input voltage and it could also use the current led if you feed the led a 50% duty cycle output to produce the orange color along with high for red and low for green and change the pin driving the led to an input pin to turn off the led for the flashing requirement. Since you only need 2 I/O pins on the processor something much smaller than a 328 in a typical Arduino Uno) would work as long as it supports analog input pins (I'm more used to PICs than Atmel's small cpus).
Peter Van Epp