It is if it is unnaturally yellow. High pressure sodium lights are yellow orange but low pressure sodium lights only emit yellow light. It's really odd to be in a parking lot lit only by LPS lights. Every car is a shade of yellow. It's the closest thing you'll ever have to seeing in black and white.
HPS is easy. It's LPS that's harder to get. Plus I heard that disposal of the bulbs are difficult as they tend to explode if the sodium comes in contact with water...