you can add the separate eyecolor makeup region (and presumably any modded custom clothing slot) by going into the mod folder in:

Steam/steamapps/workshop/content/108600/3228005270 (or just searching fashionista if you are lazy like me)/mods/fashionistaPatch/media/lua/client/fashionista

and editing the lua file in notepad. From there you can use the structure the patch author used for the custom equip region's name.

For KATTAJ1's eye color being:
FashionistaClothingGroups.MakeUp_KATTAJ1_Eyes = {
locations = { "MakeUp_KATTAJ1_Eyes" }
}

Thanks to the people that made this patch for making it rather easy to add fixes for modded clothes slots like this. The formatting they used for it was very easy to understand even for someone scared to even touch lua code, and I doubt I would have been able to as easily looking through the original mod's files.