Lip tattoos are meant to enhance lips, not create fullness. The procedure is designed to define lips, not to create volume.  It gives you the appearance of a full lip.  It is all about the illusion.

To create the a fuller lips, an outline on the border of the lip will be created follow by colour shading down into the middle of the lip to give it more of a blended look. The interior part of the lip will not be tattooed or will only be shaded with lighter colour

The more natural the colour, the more frequent you will require a touch up.

Years ago, permanent make up (PMU) was applied with regular tattoo ink and it often looked so unnatural.  With semi permanent make up (SPMU), the pigment used is normally thicker, so it gives more natural powdery finish.  However, it does exfoliate out of your skin after 12 to 18 months. Since you eat and drink with your lips, it is going to fade faster