I’d argue that the Tau aren’t necesarilly evil, and while I haven’t read as much of the fluff behind the Eldar, they do not seem necesarilly ‘evil’, sans their drive to reclaim worlds lost during ‘The Fall’. Now, there are the theories you can bring forth that have been floating around that the Ethereal have a more sinister alterior motive, or the other one floating around that the Necrontyr (or the other ‘ancient’ race that are mentioned occasionally in Necron and Tau fluff) are responsible for geneticly altering the primitive Tau to evolve at such an accelerated rate. Personally I don’t subscribe to the latter theory, but I do partially subscribe to the sinister ethereal theory, perhaps mostly because of the change in artwork and miniatures that came with the Tau Empire codex.
As a result my Tau army I’m building up is essentially a seperatist enclave not too dissimilar to the Farsight enclave (Perhaps a bunch from Vior’la inspired by Farsights teachings) that split off and went their own way, roughing it in the oxide deserts against the Orks and eeking out an existance allongside the few human colonies and travelers. Plenty of big knives hanging off belts, plenty of dented in shoulder pads (or none at all), lots of bare heads, and a rather motley assortment of humans and tau fighting side by side. Lots of converting work to be done :).
Raichase, RPharazon, you’ll of course see photos of the miniatures when I get more assembled. I’m waiting on the foundation paints before I start painting, I want the armor colour to be mechrite red and the clothing to be bone white, with bone white picks on battlesuits aswell.