Using the Dark theme (on macOS without system dark theme at least), the new UI do not seems well unified.
Tabs have one background color
Folder pane another
Quickfilter toolbar another
...

Finally, tab looks like a bit floating and not related to all the bottom UI.

(In reply to Nicolas Mandil (:NicolasWeb) from comment #0)

Created attachment 9320159 [details]
TB UI should be more unified with Dark Theme, colors.jpeg

Using the Dark theme (on macOS without system dark theme at least), the new UI do not seems well unified.
Tabs have one background color
Folder pane another
Quickfilter toolbar another

I would think at least part of that is intentional, to be able to visually cue into discrete sections of the screen (and what is contained in them) that are not related to what is next to it.

(In reply to Wayne Mery (:wsmwk) from comment #2)

I would think at least part of that is intentional, to be able to visually cue into discrete sections of the screen (and what is contained in them) that are not related to what is next to it.

Don't misunderstand with what I'll write next : I really don't want to go back to TB 102 UI ;-)
In TB 102, it was easy to visually distinguish every section of the UI (even a bit too much maybe). And the colors' cascade from top-left to bottom-right (reading way) was consistent. (I add a TB 102 capture to make it more obvious)
That's not the case with the actual colors of Supernova: it seems a bit messy and it mess me a bit. I need to concentrate more, the UI attract or stop more my look.

I hope it's more clear and help.

Not really important enough to be a defect. Perhaps room for enhancement.

This is tricky to achieve because as you can see from your screenshot, those tabs are not always above the same element.
The folder pane (or any other pane) might be in the middle of the selected tab, and the color might not match.
Matching those colors means having those content panes all with the same background, and we don't want to go there otherwise we will lose the visual rhythm that separate the various panels.
Leaving it open with a P5 if any contributor wants to experiment with it.