Is there a way to lighten up a drawing for coloring without redoing linework?

Okay, so I was drawing away, and in the end I flattened the entire picture and kept working on that layer until I was finished. But now I don't fully know how to get it lightened up to color it without losing the progress I had on the lines and such. Does anyone have any helpful ideas? Here's some before and after images, and the PSD just to see if I can help speed along a solution. Thank you, guys!

http://imgur.com/NO31rEd

http://imgur.com/XM70JDL

https://drive.google.com/open?id=0B3UgY2683qdSbnRsb1hPV2l1VDg