Warhammer 40k: The Tau

Our enemy for this week were the Space Marines.  Ultimately, when we design a race, we have to test it against them, because they're the most balanced.  We introduced flying mechanics, but we still lost, because orks always lose, but I still had fun.  I'm looking forward to next week when we actually pitch our races next week.  For my race, I'd like to pitch something like the Tau.

The Tau are a race of xenos(aliens) that specialize in mech warfare, that is, they use giant robot exoskeletons to fight.  But the most interesting part of them is that they're probably the most morally superior faction in the entire Warhammer 40k canon.  They believe in a concept called the Greater Good, which means that they will take any action to make sure that the greatest number of people survive.  They're not xenophobic or ultra religious like the humans, nor violent or capricious like the orks and eldar.  The catch is that you might be killed if you don't agree with the greater good.
I'd like to design a race that is more morally gray and non-monolithic than the other Warhammer races.  It's almost a personal rule, that I will not design a race with a single good or evil alignment.  There's just to many interesting stories you can tell with a morally gray race.