An important part of achieving great wet sanding results is to use dry guide coat liberally between sanding steps. This makes sure you don’t miss any scratches, and helps keep you from over sanding and taking more material off than necessary.
For dark colors, there is white guide coat. While there are colors that white guide coat needs to be used with, it is not as effective as the black guide coat. The white version comes off easier.
Almost always try a small area with black first. Even if it’s harder to see, it still might work better than white guide coat. As with the blue car pictured, for some reason the black guide coat was very difficult to see, so white had to be used. No matter what, use guide coat. Just know that the white version isn’t quite as good.
Mirka is the dry guide coat recommended.