I can't reproduce it, either you didn't install the modmod correctly or I must have forgotten to include a file or something.
The tooltip in your screenshot is more transparent than in my games, yours also have alternating lines which it shouldn't have either.
Edit: I checked the three plot help relevant files, and I included latest version for all of them, I think you didn't install the updated resource folder files...
This one was changed in latest update: C2CTheme_Custom.thm
Do a clean install...
Thee pics below shows how the tooltip and plot help should look like in the latest PPIO version.
▬ Plot Help ▬
View attachment 510440
▬ Tooltip ▬
View attachment 510441