You both have convincing arguments I'm thinking of keeping Be'lakor in his default colours as he is technically separate from any particular force, and it would be something quite different to paint, but I want to link him to the army with more than the base scheme. Some armour and details in melon should work here I think but I'll be deciding once I get there. Plus I'm hoping that since others have their Dark Master already perhaps I might glean some inspiration from seeing theirs soon?
I'm busy working on the Defiler for my CSM but I feel the call of daemons strongly... So many projects, so little time - the one thing Tzeentch can't change