Crie e abra seu arquivo de idioma da fortuna:
sudo touch /usr/share/gtksourceview-3.0/language-specs/fortune.lang
sudo -i gedit /usr/share/gtksourceview-3.0/language-specs/fortune.lang
Cole o seguinte:
<?xml version="1.0" encoding="UTF-8"?>
<language id="fortune" _name="Fortune" version="2.0" _section="Markup">
<metadata>
<property name="mimetypes">text/plain</property>
<property name="globs">*.</property>
</metadata>
<styles>
<style id="at" _name="@ sign" map-to="def:constant" />
<style id="percent" _name="percent sign" map-to="def:comment" />
</styles>
<definitions>
<context id="fortune">
<include>
<context id="at" style-ref="at">
<start>@</start>
<end>$</end>
</context>
<context id="percent" style-ref="percent">
<start>%</start>
<end>$</end>
</context>
</include>
</context>
</definitions>
</language>
Verifique se está acessível:
sudo chmod 0644 /usr/share/gtksourceview-2.0/language-specs/screenplay.lang
Reinicie o gedit.