This happens intermittently, but when the user selects text, then goes to the drop down to select a different font, the drop down,
will be 'invisible' meaning that the drop down show up even with the right arrow that brings down another sublist, but
the font names are all 'invisible'. Also occasionally the selected text will 'go invisible' as well.
What operating system? If it's El Capitan, it's completely unsupported and the best advice is to roll back to an earlier O/S.