If you've upgraded from DOpus 8.x, you might find that your lister treeview has all the labels displayed in black - at least, it did for me. In this case, one of the easiest ways to fix it would be to go to Settings - Lister Themes and apply the default Plain Theme. It will reset any colour/theme customizations you might have done but the lister treeview will display properly now 
Other relevant settings in Opus 9 for controlling the colour of things in the folder tree:
Preferences - Display - Colors & Fonts - Other Colors - Folder tree
and
Preferences - Listers - Folder Tree: Use configured file display colors for tree items.
Another one
If you have a lot of files in a folder (this particular one has 1162) and you are in List view and you use the Find box to quickly find a file, soon after you stop typing and the find box gets taken out of view, the file display gets re-arranged as well and the file you had just found is removed from sight. Very annoying 
I've already reported this via the Support page but did forget to mention I was in List view. I don't have a workaround except to not use List view. Hopefully, this gets fixed soon
There's a fix for that in Opus 9.0.0.1:[ul][li]...[/li]
[li] The popup find field now appears over the top of the file display when in List mode and horizontal Tiles mode - this prevents the list items being rearranged when the field appears and disappears.[/li]
[li]...[/li][/ul]Full list of changes here: [Directory Opus 9.0.0.1)