Is it permissible to use mixtures to restore the natural color of the face after sun-darkening, or is that forbidden? And is changing the skin color to a slight whiteness while caring for it to get rid of acne scars considered forbidden?

There is no harm in using creams to remove blemishes or restore the natural skin color, as well as to remove pimples and scars from the face. A change in skin color does not necessitate prohibition, as the rule is that "what is dependent is not singled out for a ruling," and "what is tolerated implicitly is not tolerated explicitly."