Combine a small amount of dish soap with warm water and wash the leather couch with a damp sponge, being careful not to get it overly wet. Ensure that all dirt and grease is removed from the couch, as it may cause the dye to fail.
Apply a coat of leather prep solution to the sun damaged area of your couch using a soft cloth. Scrub the damaged area vigorously so the surface pores of the leather can open up to receive the dye. Dry the area thoroughly with paper towels or an absorbent cloth before continuing.
Sand the sun damaged area of the leather with fine grit sandpaper, very lightly. Do not over sand or sand across the stitches of the couch. Lightly abrade the surface of the leather so the dye will have a surface to grip. Wipe away any dust with a damp sponge and allow the leather to dry for 15 to 20 minutes.
Apply several coats of leather color to the sun damaged area of the couch with an applicator sponge or a sprayer. Use light, even strokes to avoid leaving brush marks or bubbles. Allow the leather to dry for 15 to 20 minutes in between coats. To speed the drying process, you can use a hair dryer set on low heat. Avoid touching the area unnecessarily for 48 hours after the color is applied to keep from damaging the new finish.