I have tried this and it works, I know because my nephews used to love to pretend they were rembrandt and use my white walls as canvas. Get a Magic Eraser(Mr.Clean), a bottle of regular clear Isopropyl alcohol and some hairspray. First spray the hairspray lightly on the ink and wait about 45 seconds, then gently and lightly wipe the ink stain in one direction, the same constant direction, until gone. Wait 5 minutes and take a cotton ball with alcohol and dab the area where you used the hairspray. This prevents the area of the wall from discoloring. All done.