It looks like there's a slim piece of plastic atop the tach (in the tach housing)... almost like it's red in color like it's a lens. Does this illuminate somehow? Just curious.... this is my 2nd weekend having the Mini and it gets better with every drive.

 

I believe that's the integrated alarm light. If you had the OEM alarm, that would flash when armed.

 

Even if you don't have the alarm option there is a light sensor in there that controls the dash lights.
In bright daylight put your hand over the lens and watch the 'candy corns' on the fuel gauge go dim.