Sorry for the massive delay. I haven't used filebot for a few weeks and I guess I didn't have the email replies enabled and forgot to check back in.
The issue seems to be the text focus color, rather than the text color. Grey text is normal in Dark theme, but selected items will switch to white text, when in focus / selected. But that seems to be not happening in your environment.
I can confirm that the text color does not change to white even after matching.

You could try switching to the GTK LaF implementation:
The "System" theme changes it to the light theme (white background) and colors work fine with that (blue highlight and black text).
What are your system font color settings? What text colors does Dolphin use?
Font color settings are set to "Breeze Dark" (I believe this to be the default dark theme of KDE's Plasma 5). Dolphin uses a blue highlight and white text.
FileBot r9827 may fix the issue.
Is there a way to test r9827 on my system or will it just be on the next program update?
(I'm fine with either. This is just a minor annoyance and obviously doesn't prevent me from using the program.)
Thanks for looking into it!