Hello there!
We are a Junior Team, playing at RoboCup Junior Championshit.
Our robots are playing Soccer on a Green field with White Marks.
Our Problem: Since the AMS TCS3103 Sensor is not on stock anywhere, we don't find a matching Sensor.
We are sadly not allowed to use IR Light so, the Sparkfun Line Tracking modules is not working for us.
I guess this depends of where you are in the world. Just search "Arduino color sensor" on Amazon or Google. I found different models in the US, UK and Germany Amazon store.