To restore the whiteness of your gutters, you can use a solution of warm water and a mild detergent or a specialized gutter cleaning solution. Apply the solution with a soft brush or cloth and gently scrub the gutters. For tougher stains, a mixture of vinegar and water can be effective. Rinse thoroughly with a garden hose after cleaning. Avoid using abrasive materials or harsh chemicals that can damage the gutter’s surface.