It is nice to be able to change the icons in DT, but there is a problem when you use Light Appearance during the day and Dark Appearance in the evening. Especially when the icon is monochrome, the icon will be nearly invisible in one of the modes.
A nice solution for this problem is used by Bear. You can right-click on an icon and a popup will appear with a variety of icons to choose from. These build-in icons look good in each appearance.
This would be a nice addition for DEVONthink.