Even with “Reduce transparency” enabled, Mojave’s desktop-tinting is quite horribly annoying, in both Light Mode and Dark Mode (regardless of accent color). Switching to a solid red desktop background, for example, results in this ugly appearance of the Dock, notifications, some popups, and the Finder sidebar:
An earlier answer claims that using Light Mode or using the Graphite accent disables desktop-tinting, but that’s untrue.
Is it possible to disable desktop-tinting with Reduce Transparency in macOS Mojave?
I reported this as bug #44861849 to Apple, and they closed it as a duplicate of bug #43428401 on 2018-10-19, which is open as of this writing. However, I encourage others to create bugs, as it may increase the priority if more users report.
This is still an issue with macOS 10.14.1.