Hi Macca, your screenshot is made on a Mac supported by the version 4? The iMAC running Mojave?
Do you maybe have installed there extensions changing the colours of your Mac?
Anyhow, you can try detaching the inspector from the main window. According to our support system, we've informed you about this option in our last reply. In case you've missed it:
To detach the inspector to the main window,
- call Merlin Project > Preferences > General
- and select for the Inspector Position the option Separate window
Does this help?