You should be able to buff the gelcoat to blend in. 2 things may make the repaired section look different, 1st the quality of the repair itself & the fresh gelcoat may be more glossy than the older faded gelcoat. Generally when the boat is made the gelcoat is sprayed on to a very smooth waxed mould than after drying the fiberglass is layered with the supports to the inside. After this drys the mold is removed. In repairing you are actually working from the opposite direction as the oridginal construction.
Good Luck