Use the tracing pen to trace over the lines when you want to change the line color. You can make the tip large so that it will cover the lines as you trace. It will only change the color of the lines without changing anything else about them.
If you hold the shift key down when you touch the tracing pen to the line then all of the adjacent lines will instantly be painted to the selected color. If you want to trace a lot of the lines but not all of the lines you can trace over the points at each end and then shift click in the middle to change the color of the line between the those two points.