Blends subtle wrinkles and spots while maintaining overall sharp focus; controls contrast; and adds a soft glow to highlights. 

There is basically no difference. 

The effects are different. Classic Soft reduces image contrast through diffuse reflection from built-in microlenses, softening highlights while preserving more detail. Highlights appear slightly diffused but not overly hazy. Black Soft uses a black particle solution as a glue in the gluing process, preserving shadow contrast while making highlights appear luminous, giving the image a more cinematic feel. Black Soft can be thought of as an advanced version of White Soft, and the two are not in direct comparison. 

Portraiture (film or vintage style), everyday scenes that require natural softening