Bit of background. Army started in 7th ed 40k as an attempt to have one army of multiple models. I then burnt out on 40k, started AoS with entirely different factions, burnt out on those, and am now back into this army.
The 40k end of this is the Smiling Skulls Space Marines, which is an ultramarines successor chapter that turned to khorne. The Chapter logo is a combination of the Khorne Skull and the Ultimarines "U" into a happy skull, or rather, a smiling skull. My models will draw from both loyalist and chaos model lines.
On the AoS end, I have the Knights of Nethys. Nethys is a deity in the Pathfinder RPG whose holy symbol is a mask half white and half black. Both the Smiling Skulls and these Knights of Nethys will have helments and head equivelents half white and half black. Mainly, I just like the paint theme. Ironically, Nethys is a god of magic, so a khorne army of nethys is pretty much sacrilege. Fortunately, Khorne doesn't exist in pathfinder and Nethys doesn't exist in AoS, so should work out.
Additionally, I have Khorne Daemons. For models, very notably, I really don't like the bloodletters in any edition. Instead, I've found that Savage Orruk/Orc models, when painted red, really fit the part well.