Thoroughly wash the wall repair areas with soap and water, as you should with any painting project. Paint should always be applied to a clean area. Also, it is impossible to match paint to a dirty wall surface.
After the walls have dried, inspect them closely in both natural sunlight and artificial lamp light. You may find, after the cleaning, the paint has faded in some areas. If this is the case, you will probably want to paint the entire wall.
Patching the wall is also an important part of matching the paint. The color appearance of wall paint is as dependent on the wall surface texture as it is on the paint pigments. Select sandpaper with grit that will mimic the old wall surface when finished. You don’t want to sand it down smooth or else the repaired area will definitely stand out.
If the wall paint has not faded to the point where a complete repaint is necessary, peel off a square-inch area of paint with a utility knife. Be sure you take the samples near the areas that need repairs because the colors can vary.
Take the paint sections to a paint store and have an experienced salesperson try to match them. Have the store stay on the darker side if they cannot get a good match. The lighting in the store is not the same as in your house, so it will look different at home.
Once the paint store has mixed a color, purchase a gallon of their matched paint. You will also want to buy a can of the same type of paint in pure white. Use this white paint to fine-tune your color match.
First, try the original paint as the paint store mixed it. It will appear darker when it is wet, so don’t be shocked when you first see it. Let the paint dry for at least 30 minutes.
If the color still looks too dark after the paint has dried, you will need to mix some of the white paint with the colored paint. Take only one tablespoon of the colored paint and mix it with one teaspoon of pure white paint. This is where you will need to keep your patience and relax. Keep repeating this process until you think you have the closest match possible.
Make sure you remember the ratio of colored paint to white paint so you can mix enough to finish the job once a match has been created.
As nice as your paint job is, you will probably always be able to see the repaired areas because you know where they are located. With the proper matching technique, though, no one else will be able to tell.