To make the inactive tabs better distinguishable from the active tab, you can use color schemes. If you go and use color-schemes already made and available for download or create your own ones is up to you. Here’s a collage showing a few made by @MOONRISE-OS and others:
Here, in this gallery, you can watch all of them in full-size instead of this collage, or download the pictures so you can see how they’ll look maximized on your screen:
This plugin allows to easily create such color-schemes yourself:
And if the schemes above are not enough for you, to find a plethora of color-schemes, I can’t present here because of their huge number, visit the so called Pling-Store:
These schemes were initially made for the Plasma desktop, but they are also working in Krita, because they use the same format Krita uses (an advantage of the huge KDE software ecosystem), and ah, okay, it is the other way around, Krita uses the KDE Plasma-Format.
Michelist
Add/Edit: I forgot to mention that they sometimes offer complete themes at Pling.com, that means packages including icons, wallpapers, new buttons, sometimes also system-sounds, and so on, everything to mod your desktop, and these have to be installed on KDE desktops to change that desktops look and feel completely. These packages can contain color-schemes, but I also found some that don’t, and you have to search through these packages to discover the color-scheme files they use (if they have one).
Add/Edit 2, just for the sake of completeness: A new collection of color schemes has been published in the meantime, they are from @ENJERUNE:
