Despite saying this mod is over I'm aware that a portion of people are using it and I'm making one last update to include gen3 version. Check the files tab.
The download consists of PSD files with: - 8 Designs - 4 Sample color effects for each design - 3 Sizes per design: Large (original), Medium - placed over the womb and Small - placed at the pubic area
Those will generate a color overlay you can put above your skin textures, which you should use as base layer. The mod provided "as is" and is intended for advanced users.