Is It A Radiator Problem... Help Needed.

Doing routine, check, I found that the coolant tank was empty, that was three weeks ago. I took it to the dealer and coolant was added.  I was now observant checked again in a week's time and it was nearly empty.  On Monday I checked again it was nearly empty.  This was never a problem since I acquired the bike. 

My engine does not over-heat at least according to the controls.  The radiator has water in it -- full. My fan is working. 

I am baffled by this problem. Is it possible that the radiator or some hose is leaking but very little.  There is no obvious sign of leaking though I now remember seeing a green colour dried some where on the motor, which could only have been coolant.  Any help is urgently need to solve this problem.