Colour Sanding / Polishing:
Years ago it was called colour sanding because automotive paints were single-stage (primer and a colour coat) and when the finish faded from ultra violet radiation (UVR) exposure, sanding off the oxidized paint thereby exposing the underlying paint would bring back the paint surface colour. Then, as now, most sanding was done wet so the terms colour sanding, wet sanding and as all these process involves a sanding block, block sanding all became interchangeable whether you were sanding for colour or for a level surface.
The secret to a Concours d'elegance winning paint finish is colour-sanding (before wet-sanding paint show vehicle owners often have an extra 2.5 mils to 3.0 mils of clear applied).
This kind of work should only be undertaken by a very experienced enthusiast or a professional detailer; experienced in colour-sanding (wet-sanding) more so than detailing, as this is more a paint renovation technique that takes years to perfect.
The paint sections / panels that are difficult and involve risk are usually those that are close to the edges of a panel (as this is where the paint is usually thinnest) or highly contoured areas. Flat areas like the trunk, hood or roof involve minimal risk.
For more information see the “Colour _ Wet-Sanding” article; one of a collection of detailing articles I’ve written for DetailingWiki; a series of informative, knowledge based, unbiased articles dedicated to automotive detailing