This is the recipe that I have been using for my Emperor's Children!
Credit to DarthCosiCat for inspiration for a lot of this.
https://open.spotify.com/playlist/78dT3mvp7DBOY1pDd0aaST?si=2qGxmrqtTIGpE8acRLV5_Q&pi=vurLUSdlROezm
Wash the undersuit and the bolter with Nuln Oil to dull the shine and darken them up
Apply a thin layer of Abaddon Black to the undersuit
For the black armour/gun casings/etc. I use a 2:2:1 mix of Black Legion , Black Templar , and Contrast Medium . Apply it with a wet brush so that you get thin, smooth layers. Apply more layers until you achieve the effect you want.
Base coat the armour panels you want to be pink with Emperor's Children .
Paint the pink armour again with Fulgrim Pink . Use multiple thin layers so that you can get it as smooth as you want it, or you can have some of the dark pink showing through if you want too.
Paint the leather (Belts, straps, pouches, holsters etc.) With Wraithbone . Make sure you get a nice even coat.
Paint all of your gold bits with Retributor Armour , best practice is use multiple thin coats to get a shinier metalic effect.
For any pink cloaks/weapon grips, you want to use Screamer Pink , or if you want the pale green cloaks then start with a base coat of Corax White (stay with me here)...
Go over the gold again with a couple of thin layers of Liberator Gold to make it pop.
Pick out some of the smaller details like shell casings, syringes, and grenades, with Runelord Brass
Paint the Marines flesh and any flayed skin with Rakarth Flesh , add this point i normally highlight the marines skin with Pallid Wych Flesh too, just so it looks different from the dead stuff.
Big Warhammer 40k fan, especially all the slaanesh stuff. Not an expert by any means, just sharing the recipies and techniques I find effective :)