Bodywork help!
 

Well, basically im trying for the first time to repair some rust damage on my car as it is getting pretty bad. Ive so far sanded to the metal and gotten rid of most of the rust and have just put body filler on and smoothed that out. I think it turned out decent for a newb, but to my problem now. How do i blend the new and old colors together? Being that my car is 10yrs old, the paint is faded. After spraying the primer, do i just spray with a bit of overspray on sides then wet sand it? Then clear it with some more wetsanding? Whats a good grit for that? Ive got some 3M 600 grit wetsandpaper, will that work? That seems like the common sense thing to do. Any other ideas? Thanks.