It's hard to Repaint a certain area of car to match the rest of the car. Even with the original manufacturing paint supplier and paint code, due to paint mixing procedure slightly difference between batch, the color will be slightly different.
Therefore, to proper paint a certain body panel, blend finish other panel is needed. Example, replacing and refinish(repaint) front bumper will need to blend both front fender. If blend is done correctly, it will be hard to tell.