Clean? You clearly need more faces on your armor, and maybe some hands impaled on spikes. Ave Dominus Nox!
As I know, they don't like the idea of Chaos mutations, as Chaos Gods blessing. So, genetically they are clean.
Aaah, I thought you meant as their armour. Though i think their dislike for mutations might be only for certain warbands, like Talos's.
Indeed, the decent part of them dislikes mutations and the like even when being warped in the process. The old Raptor look? That wasnt a fashion statement. It is said that a currently unknown god (or a lower tier warp entity) molded their shape into the birds of prey we can see flying about, so thats not a look they sport by choice. Also the legion contains Warp Talons, one of the epitomes of how far mutations and your sanity can go. To add to the irony Warp Talons are known to be marked by the gods often, the same gods the NL dont like worshiping. So no, far from the purest legion. If anything TSons are the purest cause most of them became ashtrays.
I saw references about purity of their gene-seed in different sources. Talos's warband was just one of many.
