default text is:

[{
  "GroupName": "default",
  "Priority": 0,
  "Title": {
    "Text": "[Player]",
    "Color": "#55aaff",
    "Size": 15,
    "Hidden": false,
    "HiddenIfNotPrimary": false
  },
  "Username": {
    "Color": "#55aaff",
    "Size": 15
  },
  "Message": {
    "Color": "white",
    "Size": 15
  },
  "Format": {
    "Chat": "{Title} {Username}: {Message}",
    "Console": "{Title} {Username}: {Message}"
  }
}]​

I recomming you to use the betterchatmanager.exe which can be download at the plugin page this program is only available on windows this program works great i'm using it to and i don't have any problems with it 

Did you save after adding them?