KDE Plasma 5.12.6 KDE Frameworks 5.47.0 Qt 5.9.6 Inkscape 0.92.2 kde-gtk-config 5.12.6 breeze 5.12.6 breeze-gtk 5.12.6 I'm using KDE, my theme is Breeze-Dark for both KDE and for GTK+ applications. When I run Inkscape via Alt+F2 or from the application menu, it launches with correct theme colors and I can see tooltips clearly - they have white text with a dark background. If I click on an SVG file in Dolphin and Inkscape launches, some colors and theme elements are incorrect, for example the tooltip has white text on a light background, which makes it unreadable.
Created attachment 113960 [details] KDE System Settings - Color Scheme
Created attachment 113961 [details] KDE System Settings - GTK+ Theme
Created attachment 113962 [details] Inkscape - Correct colors when launched directly
Created attachment 113963 [details] Inkscape - Wrong colors when launched by opening SVG
Notice that it's not just colors but also widget spacing.
Not that there isn't clearly a bug here, but what happens if you check "Prefer Dark GTK Theme" in the GTK theme settings window?
Created attachment 113997 [details] Inkscape - Wrong colors when launched by opening SVG with Prefer Dark Theme enabled Inkscape 0.92.2 2405546, 2018-03-11 With "Prefer dark GTK3 theme" enabled and applied.
Changing status until we find someone who knows how to investigate this issue.
Is this still an issue with Inkscape 3.0 which uses GTK3, when run in KDE Plasma 5.19 or the 5,20 beta? I can't reproduce it.
Tested Inkscape 1.0 in KDE using Breeze Dark, using Plasma 5.19.4, Frameworks 5.72.0 and Qt 5.15.0. No longer an issue - Inkscape launched both ways shows the same correct colors with clearly visible tooltips.