To fix a deep scratch, the whole panel will be repainted. Color matching depends on the skill of the painter.
Other than that if the paint used is of good quality, you won't see any difference in the long term. But if poor quality paint is used, color difference will appear later.
I remember I got my Coure door repainted from Toyota dealership and the work done was so professional that no one was able to judge it when I sold my car. Even though I told the person to whom I sold the car that the door is repainted.
Another example is of my father's Cultus whose door was repainted from Suzuki dealership and everyone was able to find it's repainted.
I can't comment on the skill of Kia dealership or someone outside. Get reviews from someone who actually got the job done from them. If you are not confident enough, you may be able to improve the look of the scratch using touch up paint, sanding, and compound. It won't be 100% fix, but it will improve a lot.
