with the coloring style for the editor that I had once picked, anyway.
That extra line is superfluous no matter how you color it - IMO!

I use Green and find it quite useful:

Cheers.

First of all - evidently it is on my machine, with the coloring style for the editor that I had once picked, anyway.

You didn’t share any info about what theme you were using, so one can merely discuss the “default” setting for the program, which is as I show.

A tab being active or not should not present itself with different surface features/patterns as an indicator, as if it were something that it wasn’t before, that’s just silly - IMO

Sure, you said IMO, but is it that hard to put yourself in another user’s place and see that it could be valuable to some?
However, that’s why the Notepad++ is configurable – to try to meet everyone’s need.

The way I use the program: I find the default background coloring for inactive tabs to be too dark (to be able to quickly read them and find the tab I need). So I set the background color for inactive and active tabs to be the same. Thus the thing you are objecting to is super-valuable to me as an active-tab indication.

First of all, by default it is “orange”, not “red” and isn’t all that obtrusive IMO.

First of all - evidently it is on my machine, with the coloring style for the editor that I had once picked, anyway.
That extra line is superfluous no matter how you color it - IMO!
A tab being active or not should not present itself with different surface features/patterns as an indicator, as if it were something that it wasn’t before, that’s just silly - IMO.

Thanks for showing where to find it.
Setting the foreground the same as the background gives a sensible outcome ;)

First of all, by default it is “orange”, not “red” and isn’t all that obtrusive IMO.

Second, change it via the Settings menu, then Style Configurator… to be some color you like: