Cool little demo i put together, basically uses the lamp distance to calculate how visible the object is, and uses the lamp’s colour with the original texture to allow you to change the colour (through the lamp colour field).
PROS: The setup is all nodes except for the:
-spawning
-movement
-scaling animation
CONS: You need a seperate lamp for each spawner, to ensure it has full colour/visibility.
Picture:
alphalamp try.blend (733 KB)
Enjoy! 
