Our current presence plasmoid uses standard oxygen icons and does not really fit the rest of icons in systray, which are all monochrome. These monochrome icons are defined by Plasma theme. The task is to update our code to load the monochrome icons if they are available, or use the current oxygen ones if not. All needed steps are written down in the bugreport (look at comment #14). https://bugs.kde.org/show_bug.cgi?id=302993