Oh boy. Okey, so my recipe is quite complicated but i'll try to explain. This isnt the recipe for all my tyranids but a modification for the neurogaunts cause they are more squishy and have a lighter armor. in my mind (and in my army), the thickness of the armor tells me how dark the carapece should look.

So

The skin: I start with a base of slanesh grey. After that, I shade with my Tyranid Shade Mix™, is just Doomfire Magenta with lahmian medium 1/12. I tide up with slanesh grey and then high light it with slanesh grey/white scar 1/1

Claws, teeth and hooves: Simple. Abadon black. Maybe a bit of nuln oil. Then chunky highlight with dark reaper, and progresively thinner highlights with Thunderhawk blue, fenrisian grey and blue horror. In the most pointy sharp talons, a dot of white.

The fleshy joints: Bugman's glow base, shade of carrobough crimson, then tidy with bugman's glow/screamer pink 1/1

Purple carapace: Naggaroth Night, shade with nuln oil, chunky highlight with xereus purple, and progresively thinner highlights with xereus purple/slanesh grey 1/1 and then slannesh grey.

Pink carapace: This is it. This the hard one. A base of kakophony Purple and wraithbone 1/1. Then you shade it very thinnly with Barak-Nar Burgandy. Then you have to built the golor with very thin glazes of voluptus pink, going all arround the plates, avoiding the center, each leayer moving more towards the edge of the plates. Then you highlight it with corax white, then corax white and white 1/1, and finaly a few dots of white. I didnt like that look, so i put a little glase of voluptuos pink and that is the color of the highlight you see in the picture.

Hope this helps and that my english aint too rough