Transport from the Central Railway Station or from Nanjing Airport?

From the railway station, you can take the subway line 1 to the Xinjiekou Station (CNY2). Take the Exit 6 and walk about 550 yards to the square.

From the square, there is no direct transport mode. You need to walk to Xinjiekou Station to take the subway line 1 to South Railway Station (CNY3), where you can take the airport shuttle bus line 2 (Chengxi Line, CNY20) or Airport Subway line to the airport.

The most common taxis there are in yellow, and they are operated by Dongfang Taxi Company, which is reliable.

There is no big difference between them, it is just for traffic control in regions, which is more helpful for transport management.