I would definitely check the manufacturer's P-sheets before color sanding the basecoat. All the PPG BC/CC systems that I use say to never sand the basecoat prior to the clearcoat going on. They say to even be careful when using a tack cloth. Even the slightest sanding scratch will be magnified by the clearcoat. If the basecoat is sanded, it is recommended to hit it with more base prior to the clear.
For great info on painting, go to
www.autobodystore.com. It is a great site with many helpful folks....just like this site.
Take care,
Bruce