You can play with below code after putting it in EXTRA.LESS
/* Tiled View of Forum Statistics - Start */
Simply use one of my following add-ons
Now you can change the XF default user online indicator with any FA icon, as well as its default color.
TIP : Some sites may need to run add-on rebuild option manually if they will not get proper results of icon & color re-change (2nd time change).
That.s All :)