I find that if I hover my mouse over an unoccupied area of a DisplayFusion taskbar on one of my secondary monitors, the opacity increases, that is, the entire taskbar darkens. This type of reaction is not seen on the primary monitor Windows 10 taskbar or on my Windows 8.1 / DisplayFusion 7.2 system. The empty taskbar area retains it original opacity.

This darkening of the empty area on the DisplayFusion taskbar also occurs if I hover over one the the shortcuts I have pinned to the DisplayFusion taskbar. Normally, hovering over a pinned shortcut lightens the background behind the shortcut icon. With DP 7.3, it appears that what is happening is that the icon background remains the same while all the reset of the taskbar darkens.

I am using DP 7.3 Beta 5 and Classic Shell. Attached is an image showing my DisplayFusion Settings for the taskbar