I found this great camo technique in an ancient White Dwarf, when the magazine still really tried to make us all better modelers. Check it out, you could apply it to a lot of different models, but it works well for the Tau.
1. Spray paint. I stippled with green
2. Stipple with a lighter color
3. Stipple with an even lighter color. Try to put it all over, not on top of each other too much.
4. Now the hard part, cut up tape and start working!
5. Spray paint with your second color. I used Aircraft Grey from Tamiya, which comes out as a light Bleached bone. Pull off all the tape. The pattern looks interesting, almost like it is in transition, changing appearance.
6. Paint the rest. It took me forever the paint the rest of this model, filling all the grooves with wash and lining all them with light paint. Very time consuming.
8. one drawback to masking tape: it leaves little blips on parts of the model. I am not going for a Golden Demon here, so it's cool, but I do want to warn you.
Hope this inspires! Give it a try, it's fun and would look good on Guard as well!