I would like to know this as well , how to add the possibilities to ad dmore warpaints ?
Well, adding more warpaints is easy in the CK if you're OK with editing Races. You need to make your texture and make a new Texture Set in the CK (this is for adding more complexion types, like freckles, wrinkles etc). Then edit the race you want to have that available for. In the "Tinting" tab, warpaints are stored in the Tint Layer section, and Face details like complexion, freckles etc, in the Face Details Texture Set List.
I haven't added more warpaints yet (I'm still trying to see if I can get around the USKP overwrite), but as far as I can see (by poking around CK), you don't even need to make a Texture Set for Warpaint. Just have your textures present and add them to the Tint Layer list by right click --> new. It will make a "none" entry.
Point the entry to the .dds by clicking "Choose Texture", then assign "Paint" as Mask Type.
EDIT: If you want to be able to change color on the warpaint, and have it update in real-time, you would have to add color values in the section in red http://i.imgur.com/QOJT5.jpg. As you can see, vanilla warpaints have them http://i.imgur.com/j9lz0.jpg. If you don't have those, the warpaint would still be able to have different colors, it will just not update in real-time as you change color.
I'll make a quick .esp to see how it conflicts with USKP and if the new warpaints work.
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Hey, can I make it dependent on USKP? Like making my .esp work like a "patch" sort of? By going the Wrye way of ESMify-ing USKP and having it as a master for my .esp, then reverting USKP back? Does this work for Skyrim?