SimpleWhisper is a plugin that let you whisper a specified player. It is very lightweight, it support color support (using the &a-f/&1-9 codes) and Permissions (PermissionsEx) support.
To be able to use the /pm command, you need the simplewhisper.use permissions flag.
After you start the plugin for the first time, a configuration file called config.yml is created. Simply edits between the " " how you want the PM to be shown.
{from} : Show from who the message is sent.
{to}: Show to who the message is sent.
{message}: Show the message sent.