SimCity's 24 global servers are listed in a few different states. A green light means the server is "available for all players" to log in without any wait. Yellow-green servers are available only to players who have already created a city there; everyone else will be denied entry. If the server icon is yellow, it means the server's dealing with a high volume of traffic, so players attempting to connect will have to contend with a queue. We're guessing that there's also a red light for servers that are completely down, but right now, they're all up.
Maxis is still working to eliminate server issues and get SimCity running at full speed. As of yesterday, the studio was still upgrading and adding SimCity servers, and was addressing bugs with the game itself. Maxis general manager Lucy Bradshaw told Polygon in an interview last week, "We are committed to making this right."
Keep up with the SimCity launch saga in our StoryStream below.