The icon to click on to apply the skin texture is usually in the same folder as the make-up icons. I don't know which texture you are trying to use, but the icon for loading the base skin texture is usually named "MAT [name of texture package]".

Generally, the make-up is only different variations of the head textures (V3 uses different textures for body and head unlike the P4 woman who uses one texture for both head and body). Clicking on a make-up icon just loads another head texture with a different make-up applied. The eyes are separate from the skin textures on V3. Loading an eye color should work regardless of which skin texture is loaded. It's possible to mix one skin texture with the eye color of another skin texture.