For those of you who would have ANY idea how to do this, I'm making this sculpted figure here: 

My question lies with the spider lines ON his costume.  I want to use a tool to make the lines in the fondant, but I'm not sure how to turn them black/dark grey?  I thought of edible pen, but all the ones I've seen, the tip would be too wide.  I don't want to use any type of piping if I don't have to, I feel like it would look sloppy.  The other thing I've considered is maybe a dark luster, but I'm not sure if it would tint the red fondant, too.  Argh.  Any ideas?

ADo u have a clay extruder? I Would run fondant through it

 totally never thought of that!  I don't, but I can definitely get one!  I see GSA has one, but I wonder if the hole size is small enough?