How to customize X11 font cursor

According to the documentation of [XCreateFontCursor]: > Applications are encouraged to use this interface for their cursors because the font can be customized for the individual display type. How do I actually customize the cursor generated from this method? I've tried setting XCURSOR_SIZE environment variable to no percieved effect, I've tried setting XCursor.theme: redglass in my Xresources and this changes some applications but not all, (interestingly emacs uses the selected theme in the editor area but not in the menu bars) and as I am using dwm as my window manager no configuration specific to a desktop environment is applicable.