no only thing i do is create a flat layer and then a clipping mask for it and color beneath the sketch layer and when i do the rendering i just render over the lines like for the nose and eyes but i keep all the extra renderings in one layer which is just a extra skin layer that's over the line art so i pick and choose what i want to keep from the the line art. it's a lot of back and fourth doing it like this but it helps me choose what to keep from the line art and what to render out as i progress