I'm creating some fly casting videos and want to enhance the line going through the air. It does not matter if the rest of the scene looks out of color I just need to be able to clearly see what the line is doing. Remember when Fox network first started showing ice hockey games and they made the puck glow neon colored. That's what I'm thinking.
I haven't seen the video, but I would use the Hue vs Sat curve or the Hue vs Hue. Using either, you should be able to isolate the line. Punch it up compared to the rest of the frame. This is much easier to do in Davinci Resolve btw...because you could desaturate the video, except for the line. Can't think just now if there is a good way of doing that in fcpx.