Qual é o significado de “#nnnnnnnnnnnn” no arquivo de configuração do terminal GNOME?

Question

O arquivo ~/.gconf/apps/gnome-terminal/profiles/Default/%gconf.xml contém:

<?xml version="1.0"?>
<gconf>
        <entry name="use_theme_colors" mtime="1517920383" type="bool" value="false"/>
        <entry name="font" mtime="1517920383" type="string">
                <stringvalue>Monospace 14</stringvalue>
        </entry>
        <entry name="use_system_font" mtime="1517920383" type="bool" value="false"/>
        <entry name="default_size_rows" mtime="1517920383" type="int" value="100"/>
        <entry name="default_size_columns" mtime="1517920383" type="int" value="150"/>
        <entry name="use_custom_default_size" mtime="1517920383" type="bool" value="true"/>
        <entry name="palette" mtime="1517920383" type="string">
                <stringvalue>#2E2E34343636:#CCCC00000000:#4E4E9A9A0606:#C4C4A0A00000:#34346565A4A4:#757550507B7B:#060698209A9A:#D3D3D7D7CFCF:#555557575353:#EFEF29292929:#8A8AE2E23434:#FCFCE9E94F4F:#72729F9FCFCF:#ADAD7F7FA8A8:#3434E2E2E2E2:#EEEEEEEEECEC</stringvalue>
        </entry>
        <entry name="alternate_screen_scroll" mtime="1517920383" type="bool" value="true"/>
        <entry name="background_color" mtime="1517920383" type="string">
                <stringvalue>#FDFDF6F6F3F3</stringvalue>
        </entry>
        <entry name="visible_name" mtime="1517920383" type="string">
                <stringvalue>Default</stringvalue>
        </entry>
        <entry name="bold_color" mtime="1517920383" type="string">
                <stringvalue>#000000000000</stringvalue>
        </entry>
        <entry name="foreground_color" mtime="1517920383" type="string">
                <stringvalue>#B5B589890F0F</stringvalue>
        </entry>
</gconf>

Estou curioso sobre essas stringvalue entradas:

• palette
  valor = #2E2E34343636:#CCCC00000000:#4E4E9A9A0606:#C4C4A0A00000:#34346565A4A4:…
  (Sequência separada por dois pontos de 16 destes valores de 12 caracteres)
• background_color
  valor = #FDFDF6F6F3F3
• bold_color
  valor = #000000000000
• foreground_color
  valor = #B5B589890F0F

Esses valores são cores? Em caso afirmativo, por que há 12 bytes em vez dos seis habituais?