The way I do mine. I use vallejo paints, but i dont think that matters too much. you can find
gw equivalents if that's what you are using. After a black undercoat, I do a thinish coat of shadow grey, then usually 2 thinish coats of stonewall grey. This makes it a very light looking grey. Then I apply a wash, I mix vallejos blue and grey washes about 50/50, just to give a slight blue tinge to the thing. Then another thin highlight of the stonewall grey, then a final highlight on the edges with white... Although I recently discovered p3 paints 'frostbite'. The model on the right here has a frostbite final highlight rather than white. Frostbite is almost pure white but just a hint of blue, it's really nice.
As for the predator, I'd be inclined just to paint it black with little bits of ba/dc iconography. I just like a solid, unified colour scheme across a force. Just binds it all together. Think this is possibly more important when you're talking about an allied detachment. So, yeh, I'd go with black.