This is done by using mark/endmark and recolormark facilities of jsf.
For JOE see here. For JOE project see here. For original JOE syntax files see here.
For a description about how JOEs jsf parser works, see the header of c.jsf. Another good resource might be jsf.jsf.
To enable to enhanced ftyperc without overwriting '/etc/joe/ftyperc', you may place the modified one in '/.joe/' as '/.joe/ftyperc'.