RTH should work even without hooking up the computer, it's enabled by default and should perform as intended as long as you waited for the Phantom to log the home position before taking off.
I'm sure it must be a pain for you trying to follow the colored LED patterns, when I first saw them I wondered how the color-blind would handle that. There are a number of aftermarket options available which can provide other methods of battery-level monitoring...from simple things such as loud buzzers that go off when the batt is low, to full On-Screen Displays that will show (among other things) how many sats are locked by the NAZA.
The other option might be to use color filters on the LED itself, to change the light to shades you can easily distinguish.