separating metal portions of 9V train track

[Philippe Hurbain]

I agree it's far from obvious here... It should be possible to cobble something using Edger2 engine. What it would do is accept a key color from command line, then color any line or condline with the same key color if they border one (optionnaly two) key colored surfaces. I don't promise anything yet, I have to be in the right mood to write software...