1970 Duster project in Sweden

Metalflake or metallic colors are harder to match. The reason being is the base color is somewhat transparent, with the metal flakes in it. Using a darker primer will make the color darker, lighter color primer makes the color appear brighter. Also the wetter you apply the color the darker it will appear because the metal flake will settle into the color pigment, you can also end up with mottling in the paint if metallic is sprayed too wet. If you spray the color on with lighter more dry coats the brighter it will appear because the paint tends to dry before the metal flake can settle into the pigment. For a novice setting up a paint gun and getting it to match is going to be tough.plus trying to shoot metallic colors in single stage paint is an exercise in futility.

Most body shops having to match metallic colors will go with basecoat/clearcoat finishes. They will fade the basecoat into adjacent panels to blend it in, then clearcoat the repair and adjacent panels for the shine.

Example. Repainting a whole door, they would scuff with fine scotchbrite both the fender and rear quarter panel to get the paint to adhere. They then fade the new paint basecoat onto the fender and rear quarter panel about halfway to blend the color in to trick the eyes making it match. Then they would clearcoat all 3 panels.