How to disable Mojave’s desktop tinting (with reduce transparency)?
Set your Desktop background color to pure white:
System Preferences > Desktop & Screen Saver > Desktop > Colors > Custom Color… > Color Palettes > White (double click)
Even in the “Reduce Transparency” mode, Mojave calculates background colors off the desktop wallpaper, so having white there ensures light backgrounds. The contrast with text is much better.
Also, the setting “Increase contrast” in
Accessibility > Display gives the best contrast, but it adds black edges to UI elements.
At the moment, the best option seems to be not reducing transparency and living with the blurred background. At least then, you get a tint of what's behind the app, instead of the sometimes-completely-unrelated desktop wallpaper.
Another slightly ugly option would be to use a solid gray as your desktop background.
It's really horrible. It's not really a solution, but I got round it by using 'Yosemite 3' as my desktop picture. The colour you get from that is pretty close to what it used to be.
Really hope they add an option for this soon like they did for the translucent menu bar.
Try using the 'Reduce Transparency' option under Accessibility:
System Preferences - Accessibility - Display - Reduce Transparency