I understand your concern about removing the black marks left by the selefon tape without harming your car's paint.
One method that has worked for me is using rubbing alcohol or isopropyl alcohol. Dab a small amount of alcohol on a soft cloth and gently rub the affected area. This should help remove the adhesive residue without causing damage to the paint. Another option you could try is using WD-40, but make sure to test it on a small, inconspicuous area first to ensure it doesn't have any adverse effects on your car's paint.
As for the color marks left by the ribbon, you could attempt to clean them using a mixture of warm water and washing powder. Dip an old sock into the solution and gently rub the spots. Finish off with a thorough rinse using clean water and consider applying a coat of wax for added protection. I hope these suggestions help you restore your car's appearance.
Best of luck!