It would be great if we could have an option to use monochrome icon in systray. Desktop environments like Plasma or GNOME allow to set different themes for users desktops and usually icons in systray are all monochrome. When it comes to KDE Plasma, i'm sure that Visual Design Group could provide monochrome version if someone could implement it. Reproducible: Always
Created attachment 100483 [details] RSIBreak icons compared to other systray items on Plasma desktop
The theme makers are more than welcome to provide rsibreak icons in their sets, there's nothing for rsibreak to "fix". You should contact the maker or your icon theme and ask him to provide such icons. https://github.com/KDE/rsibreak/tree/master/icons contains the icons that rsibreak needs.