Green could either mean you currently have coverage in your area or that your battery is running low.
You can disable it though if you want. To get rid of the messages indicator, go to Profiles>Advanced>Active Profile. In each option, you'll have an option to disable Repeat Notification.
For the coverage light, go to Options>Screen/Keyboard, scroll down to LED Coverage Indicator and disable it.
Posted from my CrackBerry at wapforums.crackberry.com