Hey man, still working on the temperature warning system?
I would do it like this, maybe not necessarily with arduino pins on the cathode, maybe with shift register pins, I don't recall how many pins you had committed with the temperature sensor.
Anyway the idea would be that you multiplex the LEDs - if you wanted 5 green bars, you drive the green anode high then quickly cycle thru the 5 green cathodes one at a time in a continuous loop, with enough duration and at a speed fast enough that they all look on. Maybe set the loop to go thru all 10 all time, and just not turn on the higher ones unless needed to make the intensity the same all the time.
Once the heat started getting up there, you turn off the green anode and turn on the orange anode and start doing the same thing, with more & more as the heat increased.
No matter how you do it, make sure to only turn on on LED at a time to avoid overloading an anode output.
If you are allowing size to increase, then you could consider adding 2 transistors to control sourcing current from Vcc and two SN7406s, which are 6 inverting drivers in a 14 pin package which can sink 40mA each (still thinking just one Anode on at a time), high output from arduino is inverted and turns on the LED with high Anode.
Conveniently packaged, yet will need min of 4.5V to work. I don't recall what your temp. guage ran at if you were considereng running the competed package from a 3.7V LiPO battery.