Take the cabinet doors off the cabinets by unscrewing the hinges from the doors with a screwdriver and placing the doors on a flat surface with the side you wish to paint facing up. Remember to protect the surface you are painting on by laying down a newspaper or a drop cloth to prevent unwanted stains.
Sand the surface of the doors with a light-grit sandpaper like 200-grit wood sandpaper. Wipe away the residue and thoroughly clean the surface with a typical cleaning solution and towel. Apply a liquid sanding fluid to the surface with a rag. Wipe this onto the entire surface.
Paint on the stain using a stain paint brush. Use any type of stain you like; just make sure it is darker than the original stain. Allow this coat of stain to dry thoroughly according to the drying times listed on the instructions. Usually, this is between four and 12 hours.
Seal the surface with a clear polycoat protective finish by brushing the finish right onto the stained areas in thin coats, using a paint brush. Allow this to dry as recommended; typically speaking the drying time is about four hours. Read the finish's packaging directions to be sure.