I got response from the dealer (Herb Chambers, Sommerville, MA).

They say that the MB coolant they use is kind of slitghtly yellowish ~ orange.

They added that some MB cars are OK with other maker's coolant, and that I have to look up manual for my cars.

There is a sheet of paper that came with my car (may be somewhat out-dated). It has MB approved oils, AFT, coolant part number, etc.
The coolant part number on that sheet is the same as what is on the independent's invoice. It is also the same as what's on the bottle of coolant I received from FastLane.

I will call the independent on Monday.
What shall I do if they insist that the green stuff is OK?

Some people on this board said that the indi is better than dealers, though expensive.