Using spare red insulated 10 gauge wire as a ground
Keep in mind that you can't use wires pulled out of cable because the insulation is not marked. You also have to have all splices inside a junction box.
But to answer the question, you can't use a red wire for ground, but you can strip all the insulation off the conductor because a bare wire for ground is OK.  It might take a few minutes depending on the length and the tools at hand.