Contrast is nice to a point, but consider the flow of the bike.
Painted headlight color of bike works because the color does not get sliced of at the steering neck, so that works. Your lines however are not the focal point of the polished front end, so stainless or silver will blend in and not detract from the forks. But black sticks out and pulls the eye away from the stronger feature.
Its a problem when judging bikes at shows.. Do the parts bend in and fit and go with the flow..or doesvit look like a wheelbarrow. Of parts was added to the bike , which then looks like stuff piled on top of stuff, piled on top of more stuff..
Its all about the flow.. Look at each part and think, does it compliment everything around it, or is it clashing.
I vote silver lines..