The current default Nicklist icon theme, Breeze, is barely visible when using Breeze Dark colors. A Breeze Dark compatible icon set should be created. Compatible "im-user" icons can be found in the Breeze icons-dark repo: https://github.com/KDE/breeze-icons/tree/master/icons-dark/actions. The original Breeze set might need updating as well, the current "im-user" icons look different from what is in Konversation.