I don't know what car or color or area of repair you're dealing with, but rattle-can colors will almost certainly not be an exact match.
Also, enamel & lacquer don't play well together, and you can get a reaction that wrinkles either the new paint or the old.
Never asked for an exact match in the original post, he wanted something easy and quick from the read of it. The dude is obviously not Iinterested in starting over in the area, but your response makes sense- if O.P. wants flawless, get a pro to do job. Otherwise, be at peace if you do the work and it's not perfect.
