I'm not sure if it is possible to edit warpaint from the CK. Here's a workaround in case nobody can help-
Warning: This should hide the warpaint for your NPC, but it will also hide it for Borkul as well.
You can use Fallout Archive utility to extract the .dds texture for the facetint and use gimp (download the dds format plugin) topaint over the warpaint with skin.
Open textures.bsa
textures >actors>character>facegendata>facetint>skyrim.esm
The baseid for Borkul is 0001338A http://www.uesp.net/wiki/Skyrim:Borkul_the_Beast
Extract 0001338A.dds
Open 0001338A.dds in gimp, select the base color using the eyedropper, and get rid of the warpaint using the fill effect.
If you're not comfortable using gimp, you can try extracting the face tint of another orc and renaming the dds to 0001339A.
place 0001338A.dds in data\textures\actors\character\facegendata\facetint\skyrim.esm