You always need to be careful when touching up an existing painted surface. We professional painters take extra care with this. If you find yourself needing to deal with this repair yourself, I highly recommend that you use paint from the original can but don’t use the same “strength” – reduce it by about 10% to 15% with the reducer that is recommended on the paint can’s label.
Now, the paint isn’t the only detail you must remember. How you paint it is just as important. The tool rule is fairly simple: If the paint was applied with a roller, use a small trim roller. If the paint was brushed on, use a brush.
Carefully, carefully add a small amount of the touch-up paint to the brush or roller. Slowly “feather” the edges on the needed spot, working from the outside toward the center of the area. By lightly drawing the brush across the area outside of the touch-up toward the new paint area, you’ve made a “transition zone” that diminishes the appearance of the touch-up.