This means Pi-hole is working.
This is expected.
You debug log doesn't show the option for web interface Theme. This means you are using the default one (auto theme).
The auto theme automatically selects between Light and Dark themes if the browser is configured to do so. As a result you are currently using the dark theme and the colors were changed.
Did you clear the browser cache after enabling the group?
If you did and still are seeing ads, maybe you need to block a few more domains.
I didn't understand this part... what do you mean?