Im on the OSX client. If you right click in a diff window you get this dialog...
which brings up this dialog....
If I choose the options menu (like you did in your screenshot) there is no 'configure fonts and colors' menu item. This (above) font menu is the only one Ive been able to find. It works, kind of, in that it changes the font of the right side diff window, but the left side stays too small.
Thanks!