Sparrow,
Besides colonial gaming being my number one period (next to ECW), and specifically the NWF, I'll chime in here, though late to the party!
As Mad Guru pointed out (and beat me to it), Ghazi's would be in white, as the sign of "purity". That said, what I've done for the Indian Mutiny period, is add a bit of color by a green sash for some figures (given the "green" being for jihad) or (very uncommonly) a green turban. I also did that for the NWF period as well, but even more uncommonly.
With regard to flags/standards, I go with a green background for Ghazi units (when such are used).
You can see some of my figures in the couple WI mag articles I've done thus far on the NWF, as examples (I'm sure a Ghazi unit was shown somewhere).
Have fun painting!
Regards,
Bob Giglio