The command surftransparency adjusts the molecular surface transparency to percent (0% completely opaque, 100% completely transparent) for the specified atoms. This overriding surface transparency is distinct from any transparencies included in the definitions of the surface colors, which will be ignored. Surfaces colored with tcolor will not be affected by surftransparency.
The command ~surftransparency resets the molecular surface of the specified atoms to use the transparencies (if any) in the surface color definitions rather than an overriding value previously specified with surftransparency.
See also: surface, surfrepr, colordef, the Actions menu