I think the dark streak you're seeing is the joint between the web and the lower spar.

In any case, This is what cracks me up about non-builders. They seem to think that building is a chore. Sure it can get frustrating at times, but then, so can a lot of things (women come to mind LOL). Building, for the most part is relaxing, rewarding, and FUN!

Note: I am not refering to people who don't have time to build, or can't build for other reasons other than they are unwilling to try. So let's not turn this into an ARF vs Building debate. Thankyou.