"Paint Codes" are an exact match.
The paint code will get you close. Allowing for variations in manufacturer and formulation and surface prep and environmental conditions and application probably close enough in most cases to blend, but not to panel paint - if we were talking about an automotive fender for example. But yes, for a fairing a paint code will get you close enough to an "exact match." But considering the variations in the factory paint - so might the rustoleum.
It also depends a great deal on what experience, skill and equipment you have available for the project.