Thank you all for the responses, they have been most helpful. I will be sure to tick through the list Supercourse provided with the service professional to see if there is any possibility of something besides the thermostat. As far as the questions:
The coolant has been replaced at the normal intervals as recommended with the BMW preventative maintenance and all done by BMW trained service professionals/technicians. While there could have been orange coolant used I think it highly unlikely and I'm certainly not in a position to confirm that, unfortunately.
I checked the coolant level after the car had been sitting overnight so it was definitely cooled down.
I made an appointment with my local BMW repair shop after calling the stealership and getting an estimate of $425 to replace the thermostat. My local repair shop quoted $300 as follows: $115 for the part, $165 for the labor, and $20 for the replacement coolant. The appointment is for Monday (3 days away) so I will likely get the full low down then and will post the conclusions. I am hopeful it's only the thermostat or a sensor.
Thanks again for the thoughtful, educational and enlightening responses!