For Nexus One owners, one of the lesser features of the officially released Android 2.2 is the enabling of multiple colors for the trackball. Granted, some functions like bluetooth have long had color notifications, but for the most part it has been a stark white light. Depending on what kind of device you have, there are now options to unleash the rainbow.
Rooted Nexus One
If you have a rooted Nexus, then you know you’ve had this ability for a while, so this is more of a reminder. The app for you is Trackball Alert by lilHermit.  This app gives tons of customization, allowing not only color choice but flash frequency as well. Currently supported apps are SMS, MMS, Email, Gmail, Missed Calls, and Twidroid. The pro version of Trackball Alert also offers even more customization options. It should be noted that Trackball Alert will only work with certain ROMs; currently listed as:  MCR 1.9+, MCR Desire A13+, and CyanogenMOD 5.0.4.0+.
Stock Nexus One
Blink will work on Nexus One devices that have not been rooted.  Blink offers less app customization compared to Trackball Alert– only SMS, MMS, phone calls, missed calls, battery, and memory are available, but it is still a decent application to put some color on your device. App notifications can be to  1 of 12 colors and 5 flash speeds. Blink also includes an on/off toggle for times you might want to keep things vanilla. In addition to Nexus One, Blink will also work on some other Android devices.
