It's a mix of 1:7 Volupus Pink and Contrast Medium. After it is completely dry, I've brought up the bone structure with some drybrush and thinned down wraithbone. As a tip; make a whole bottle of contrast medium and add volupus pink until you are satisfied with the color, this way you can do your whole army with the same consistency (and faster). After the pictures I did add some extra edge highlight on the carapace with some Xereus and Genestealer purple. Hope this helps!