I just updated my iMac to Mojave, and am still trying to setup my preferences.
I tried dark mode, but did not like it (half of me apps seem to ignore it anyway).
I switched to light mode, but this too has problems. The File Save dialog shows a list of Directories and existing files, but the latter are very light grey, almost indistinguishable from the background.
I have searched the Preferences menu, but can't seem to find any setting to set normal contrast levels like in High Sierra.