Created attachment 109594 [details] Image showing the issue Icons on the toolbar are not visible when the image is dark. The image clarify the issue. What about some clear background color, maybe even semitransparent? Maybe using the same color of the main app toolbar, even semi-transparent, would be ok?
Which widget style do you use ? Look in Setup/Misc. Which desktop do you use ? Which Linux system exactly ? Can you reproduce the problem with the AppImage bundle which include all the necessary files ?
Created attachment 109596 [details] Image showing the issue on mac os.
Widget style is Breeze. This is Linux Kubuntu 17.10. AppImage is identical. Same exact look on Mac OS: attached how I see it on mac. Do you see it differently?
We now use a transparent background, which improves the visibility. Maik