Thanks a lot for your advice.
Actually I let the boat yard paint it incl. the red line on the top of the hull. I think they are very professional. They wrote me:
Band waterline and band rubbing strake:
sanding the strips band waterline including the rubbishPainting with polyurethane cycle of the whole band SAME COLOR. He cannot see the original color but maybe it is possible to see it for a short after you polish it.
and It is also not cheap at all... I am almost sure that they will spray the color but I will anyway ask them to use AWL-GRIP