Comment # 6 on bug 940772 from Wolfgang Bauer

(In reply to Olaf Hering from comment #5)
> (In reply to Wolfgang Bauer from comment #4)
> > You mean in KDE's systemsettings?
> 
> In digikam settings.

Ok, that's basically the same, just restricted to digikam.

Well, I see no real difference here if I change that setting. As mentioned,
digikam seems to use Gtk+ in any case when run inside GNOME.
And the widget look like it's using oxygen-gtk, which might be a problem in
Tumbleweed because Gtk doesn't support theming engines any more.
But you probably don't have kde-gtk-config(5) installed anyway, so in your case
the configured GNOME theme should be used.

OTOH, different digikam "Themes" do make a difference, with most of them I get
black (or something very dark) text on black background. Only "openSUSE",
"openSUSEdark" and "Zion (Reversed)" give readable tooltips (I might have
overlooked one or two though).
I think the problem is that the tooltip background is always black, and maybe
also the wrong color is used for the text.

If I switch to "Adawaita" in KDE's Gtk settings, I see what you describe: the
tooltip background is always bright (beige?) and the default bright text is
unreadable. Changing to another digikam "Theme" fixes this though, except those
3 that worked before of course.

I do remember other bug reports about similar problems with the Gtk+ style,
even in KDE itself.