Updating color / Genre etc on many tracks at once?

Ok is there a way to mass update say the color of a track or a genre? or even apply a color to the tracks inside a playlist?

If there is no way to mass update information by selecting many tracks at once then how about editing the XML file for a playlist? is there an XML file for a playlist? or is there only one XML file for the entire database... can that be backed up and manipulated? I could script this if this is possible - then re import and all the new manually entered info would show up? 

Is this possible - has anyone successfully updated many tracks info at once?