Take a switch plate off the wall to see if paint extends to that area. If it does you can cut a piece off the drywall to bring to the paint store for a color. Or, get a paint deck and match it up to the wall. When you’re ready to paint, keep the touch up as small as possible. You’re just filling in enough to not go beyond the existing bare area. If the color isn’t a good match, extending it beyond the original bare area just increases the problem.

Source- I’m an artist and decorative painter for 25+yrs.