Coloring on the lines

Now that I'm back home, I'm busy in my workshop.  I've painted my grouchy old guy with an Afro skin tone and enhanced the wrinkles with a darker color.  I also painted the lips with a lighter pink color.  I still need to thin out the darker lines in the lips by repainting the pink color around the dark lines.  In fact, that partially describes my method of painting wrinkles. 

First I paint the wrinkle with a slightly lighter color than the skin tone.  Then I paint a thinner line of color that's darker than the overall skin tone.  Then to make the wrinkles finer, I touch up the edges with the original skin tone color.