How can we enhance LEX readability ?

Most of our users are disappointed by Lightning Experience interface.

The problem is not only slowness but graphic appearance of the font characters

Colour : Deep grey characters displayed on a light grey background are less contrasted, therefore less easy to read than former black characters on white background

Size in some screens (i.e : picklists) 3 font size can coexist (+ bold and not bold fonts) on the same screen. By definition if one size is tuned to the best, the wo others are either too big or too small.

Is there a way to modify all these parameters ?