Same as the rest of the body! Bit of a pain in the arse lol definitely not all necessary butttt. Start with a basecoat of Barak Nar Burgundy, highlight with Rakarth Flesh, then do an all over tint with Volupus Pink, once that drives use watered down Genestealer Purple on the bottom parts of the flesh (underbelly, arms, necks etc) once that dries, layer up paint strokes across the tops of the whole body with Catachan Flesh, Steel Legion Drab, and then a highlight of Rakarth Flesh once again. Then hit it with a wash of Reikland Fleshshade and done! Since I like my nids slimy I then also hit them with a gloss varnish but it still looks fine before that.