Find a leather dye that most closely matches the dye already on the furniture. If you have a lot of scratches or the color has faded, chose one that is one or two shades darker.
Put on gloves when working with the dye to prevent transference of the product to your skin. Also place drop cloths around the furniture if you are unable to move it outside. Open the windows to provide adequate ventilation from fumes, and keep children and pets away while dying and until the color has cured.
Moisten the sandpaper, and sand the surface to remove any waxes or clear coat and to take off rough areas. Do not sand excessively, or you will turn the leather into suede. You will see hints of the original leather as you sand. This is sufficient to have removed coatings and to open the grain.
Shake the dye well, and pour some into a glass bowl or container that is disposable. Dip the sponge into the dye, and test it on an inconspicuous place. Under the cushions or at the back of the furniture is ideal. The dye must be close enough to the original color and must not go on splotchy.
Proceed with the dyeing process if the color takes well. Wipe on the dye in small areas with the sponge. Work in the dye with a splotching technique, and press with the sponge.
Let the furniture dry for 48 hours. Prevent sitting or activity around the furniture, as the stain may transfer onto clothes and skin. After the time has elapsed, buff it with lint-free rags until the luster comes out. Use super-fine 1600-grit sandpaper to reduce built-up areas.
Buff on a leather finish or conditioner after you have wiped the surface. This will seal and protect the new dye and create a buffering finish to help prevent future drying, fading and scratches.