I will find out what it is tomorrow.

 

Back from the dealer...With the car! Great service as always. Showed the adviser and the mechanic the reservoir. Mech wasn't sure what it was initially. He had two other techs look at it. They checked the trans lines and coolant lines. No leaks. Oil looked good. Trans fluid looked good (yay). They said the coolant was old. They removed the reservoir, emptied it, cleaned it out, and added new coolant to the correct level. No charge to me. They recommended a flush in the near future.

MathNerd gets the prize for most accurate guess. =P

Thanks to all who replied.

 

Im glad it wasnt anything serious and you got it taken care off for free!