If you own a Nexus One you’ll find a few trackball colour apps around but all require root access. However, if you haven’t gotten round to rooting your device yet, XDA forum member andrewpmoore has written Light Flow an app for non-root users!
Light Flow lets you monitor a number of events and has 2 modes.
Priority mode lets you choose which notification type is most important to you and the trackball will flash in that colour. Succession mode is where the trackball will change colour and cycle through the colours of the notification types.
The modes can be set accordingly for when the phone is on charge or on battery, and the frequency of the colour cycle can also be configured.
Light Flow is available in a lite and paid version and is compatible with Gingerbread, the lite version being available for free on the Market. For more information, head on over to the application thread._________