Hey Tim!

Thats a vertex normal thing (the dark areas). If your geo is all good - verts merged and no polys inside the stucture (basic nonmanifold stuff) then you can try a few other things. Try going into the EDIT POLYGONS>NORMALS submenu and play around with some of the functions you'll find there like SET TO FACE.

All that aside, your model may render just fine the way it is.

Good luck and good modeling!

Dave