How do I change the color of lines drawn on an imported scatterplot from green/red to black and gray?

Hi Jc,
That looks like a very basic thing in Inkscape, changing the stroke colour.
Select the line and Shift+Click in the palette bar at the bottom of Inkscape.

Probably you have to ungroup the imported file first, with Ctrl+Shift+U.

You can read the basic tutorial under Menu > Help > tutorials > basic.

Good luck with it!

Thank you Kirstie.