Heres what I got from the google website on the colors for the track ball with link at the end
The status light (to the right of the earpiece) and the
Trackball change colors, flash, or glow briefly to inform you of the charging status of the phone and other important information.
The status bar at the top of the touchscreen also provides information about the phone, as described in
Monitoring your phone's status and
Managing notifications.
Status light
Status light state
Meaning
Green
Fully charged (when connected to charger)
Amber
Charging (when connected to charger)
Flashing red
Battery low
Trackball
Trackball state
Meaning
Flashing white
Incoming call.
Flashing blue
Incoming call when connected to a Bluetooth headset.
White pulse
Notification received. You can configure the trackball to pulse once or repeatedly when you receive a new notification. See
Sound & display settings.
also here is the link for this