Just to share a slightly different perspective on this.... Personally I don't understand this fetish for homogenous paintwork. Someone obsessing over this suggests a priority of resale-value over use-value...fine, if you want to make money out of bikes... I like to ride 'em.
Achieving Invisible repairs is of course highly skilled work, usually involving much expenditure of time, if you try to do it yourself, or money, if you get a specialist to do it. No doubt pearls and flams and other special finishes are even more challenging to repair invisibly. A certain sort of person may enjoy this challenge, but what you get at the end of it is a lie...It's like saying: "This bike has never been abused in any way".
The function of the paint is to protect the metal from corrosion. If I found a part of my frame was corroding, I would sand that part back to bare metal, prime, and paint, preserving as much of the surrounding original paint as possible. Mainly because I know it is much tougher than whatever I'm going to be replacing it with. I consider it more or less like mending a puncture in an inner tube, and chances are my paint repair will be just as obvious as a patched inner tube is. This approach need not preclude skill, art, or most of all, fun. To a homogeneity-fetishist, the result will be laughable...what do I care?
A repair like this, says: "This bike has been abused, and someone has taken the trouble to prevent further problems arising from that abuse", which is the truth.
Obviously, if you're planning to enter your bike in a show or something, a repair like mine will guarantee that you win no prizes. If, on the other hand, you are planning to go for a ride, it will get you wherever you are going without worrying about either your frame corroding, or all the paint-matching trouble you would be in for next time you scratched your frame if you simply had to have it all one colour.