Hello Vijay_NJ,
Thanks for using Apple Support Communities.
For more information on this, take a look at:
Alternating amber/green
When multiple Wi-Fi base stations are available during setup, you can trigger this behavior by using the Identify feature in AirPort Utility.
AirPort base stations: About AirPort base station status lights (LED)
http://support.apple.com/kb/HT4600
Best of luck,
Mario