Problem with Color in TextFilter.HTML_FORMAT

The Color is after export not correct. This is the HTML-Text after export with this code:

return TextConverter.export(_textFlow, TextConverter.HTML_FORMAT, ConversionType.STRING_TYPE);

<Font face="Verdana" color="#ff0000">  <!-- ok -->
     <span>test</span>
</Font>
<Font face="Verdana" color="#ff">        <!-- "#0000ff" -->
     <span>test</span>
</Font>
<Font face="Verdana" color="#ff00">     <!--"#00ff00"-->
     <span>test</span>
</Font>

Can you help me?

Thanks a lot....