Either copy back the back-up copy you made before editing the file.
Or if you didn't keep a backup copy, run the installer for FM again and choose the repair option and it should restore the file. (I'd advise you to backup any other files you have edited and want keeping before doing this as the repair option may delete them).
Or assuming you have only changed the profile attribute colours, adjust the following lines in the fm colours file to these (these should be the default colours):
<pre class="ip-ubbcode-code-pre"><!-- profile attribute colours --><colour name="low attribute" red="180" green="180" blue="0"/><colour name="normal attribute" red="220" green="220" blue="0" /><colour name="good attribute" red="255" green="204" blue="0" /><colour name="excellent attribute" red="255" green="160" blue="0" /><colour name="special attribute" red="255" green="160" blue="0" /><colour name="attribute label" red="255" green="255" blue="255" /><colour name="special attribute label" red="255" green="255" blue="255" /><colour name="profile extra text" red="150" green="200" blue="255" /></pre>
In future I would advise you to backup files before editing them