I finished painting my car and started color sanding,started with 600 because of orange peal then 1500, then 3000. problem is I can still see scratches from 3000 after rubbing compound, not sure what to do, should I go to 5000 grit?
Your not seeing scratch's from the 3000, it's from the 600. The problem you have is, there is to much of a gap in between your grit's. First, I believe 600 is to abrasive to start with. I start with 800 then move to 1000,1500,2000 then finish up with 2500. Each grit must be "just" abrasive enough to remove the prior grit sand scratch.
600 to 800,1000,1500,2000,2500 is where you stand now. I also alternate the direction of the sanding process. 800 is forward and aft motion then the 1000 is in the opposite direction and so forth, leaving the last grit for a forward and aft motion. This way you can track the sanding and see if you've removed the prior grit scratch. This also flatten's the surface and insure's that you won't get rut's and deep scratch's in the finish. It's just sandpaper management.
I use a three step buffing process too. Just using rubbing compound will not give you a clear deep finish.