How do I change the color of a line segment, not the whole grouping of lines?

cooper,

"I am lasercutting with this, so I need to ensure the paths are just single lines."

I wonder whether this calls for another solution that leaves the original paths as they are, or is just silly/unusable, but you might:

1) Starting with nothing selected, click the path segment in question with the Direct Selection Tool (hold Shift and click each path segment if more than one),

2) Hold Ctrl/Cmd and press C then F then X then F to bring a copy to the front as a separate path (set if more than one, and in that case also Join or Group them),

3) Change the colour as desired.

You may split the paths with the Scissors tool and recolour as desired.

Or you can make a Live Paint group for flexible adjustments.