Rigid collodion, a favorite of mine! I had to use some to get the cheek scar for this costume: http://www.cosplay.com/photo/3208066/
Anyways, in order to make it look real, you should have a nice, clean surface, so greasepaint on the bottom probably isn't a good idea. Buy a red lipliner pencil and sketch on your scar. Don't do it too dark! Next, use layers and layers of RC. I usually stop at around 5 or 6 layers, you may need more or less. RC will make the 3D shape/depth you are looking for, and you may need more or less layers. To finish it off, I bought some cheap pink/red lip gloss from the dollar store and gently paint into the scar. Trust me when I say it looks real, and you wont need to put greasepaint into the scar to make it look real.
Also, nothing removes this stuff. Just pull around the edges of the scar, and screech while ripping it off. Less layers=less pain