The following pics are of an old Trygon of mine, that I've since gotten rid of, but shows the basic theme I will be going for yet again - acid green carapace fading to black, dark gray skin, green talons/claws, and pink/purple squishy bits (tongues, tubes, etc).
I always try to focus on the two parts of the model that draw the most attention - bases and faces. I've highlighted up the face of the creature to a lighter gray, to give the model some depth. I've also done a three-color highlight on the sand of the base, and included patches of dead grass, snow, and slate to make the model more interesting and finished looking.
Below are pictures of a completed brood of hormagaunts, so you can see that the scheme is even more striking when the swarm is at full strength rushing towards your lines in a headlong sprint!
Stay tuned for more - I should be able to get some models primed tonight, and will have pictures of my first flying hive tyrant live this evening, with more to come over the weekend (I'm not going to be drinking for a few weeks - the holidays were a whirlwind of late nights and whiskey).