How can I change the folder icons or used icon-theme under linux?

[pragomer]

How can I change the folder icons or used icon-theme under linux?
Please have a look at the attached screenshot to know what I mean.

Searching for a solution for month now

[pragomer]

These icons look like Gnome's "Adwaita". So the gnome default icon theme.
Is this perhaps build-in (kind of "hard-coded") in xnviewmp, or does the program get this from the system? (in the 2nd case we should be able to change it, or not?)

[pragomer]

I tried out and installed XnviewMP under a KDE-Distro (KDE Neon).
The folder-icons that are used here seem to be "oxygen", so the (older) default-icon-theme in KDE.
( I attached another screenshot here).

So the two default icon sets are choosen:
Gnome: Adwaita
KDE: Oxygen

How can we change this ?

Bildschirmfoto_2017-08-28_08-18-56.png

[xnview]

icon theme is managed by QT libraries

[pragomer]

Pierre,
thank you very much.
So, does that mean, I - as a user - cannot change this in any way, like it is "hardcoded" in the program?
Or is there a way I could change it?

[xnview]

QT use the current theme