Are you in a highrise building? Sometimes in a highrise they use colored wiring which would not be typical to "home wiring".
Anyway following is a wiring diagram of a switch and light bulb...
http://www.make-my-own-house.com/images/ellightbulb.jpg
In the above diagram, black is connected to the switch, then to the light. The light could instead be a ceiling fan. Same wiring. In your case it sounds like they used purple instead of black.
To be clear on what color is what...
Purple connects to the switch terminal and this switch turns on the fan and the fan light?
And white is passed through and also goes to the fan and fan light?
Then green should be ground. A ground wire would also connect to the metal in a metal electrical box or the metal covering of the ceiling fan.
Now if the above is true, the big question is...
Are there several conduit pipes going to this 3 switch electrical box?
Is there one conduit pipe in which only the fan wiring goes?
So from the ceiling fan switch, there are 3 wires going into a conduit pipe and these are purple, white, and green? And these are the only wires in that conduit pipe? And only the same three colors come out the pipe at the ceiling fan electrical box?
And only the same three colors come out the pipe at the ceiling fan electrical box?
The reason I am asking is that sometimes a conduit pipe will go to several points before arriving at its "final destination". So the question is if that pipe goes directly to the ceiling fan from the switch box?