[pemulis]

AppData says 460,000 active monthly users[1]. The original VentureBeat article quoted AppData at 440,000, which is where the ~400,000 number is coming from.

Edit: In reply to the grandparent, because of the huge amount of money Color raised, they would need to make something like ten thousand dollars per user at their current user numbers to meet expectations. Since that's obviously impossible, it makes sense for them to avoid revenue entirely until their user numbers hit eight digits at least.

[1] http://www.appdata.com/apps/facebook/200067376723055-color