https://trillyke.tumblr.com/post/147792571513/hi-trillyke-i-really-like-your-style-but-how-do

( I usually use 1 pixel or 0,5 pixel line widht for that, and I use the Path Tool in Gimp).

My trick is to make two lines right next to each other - a black and a white one. This way the seam will look a bit more realistic and 3Dish. And after that I just play with the opacity and different layer modes (my fave one is Overlay mode), and there it is:

I’m still not sure this is what you asked, sorry if not. :)