Google just posted some great tips on using the Stars in your Gmail to help keeps things organized.
Stars are handy for marking important messages, but how do you mark really important messages? That’s where Gmail’s additional stars options can come in handy.
I like to use purple stars to mark important messages from my family, red exclamation points for messages that need my immediate attention, and a green check mark for messages that I’ve already taken care of but want to keep track of (ok, so we’re using the word “star” loosely here). This way your inbox can become like a to-do list.