When viewing the list of master documents at the top of the list is the Document Legend. The legend identifies the meaning of the various colours used in the document list.
Blue badge: A standard document created by LDD.
Purple badge: Someone has modified the standard LDD document at the firm. Therefore, the document is not identical to the standard, but is very close. In order to see the standard LDD version of the document, the document needs to be restored. Read this article for how to do this.