[A4] leaking yellow fluid

[Peter Kirby]

Twice now, I have noticed drips of bright yellow (almost like a day-glow 
yellow) in the snow under my 2001 1.8TQ when I move the car.  OK no 
funny comments about yellow snow....

I have gone under the car and looked inside the engine compartment but 
can't see any leaks.  The drips seem to gather in an area in front of 
the rear axle and pretty much along the midline of the car.  There is 
some minor leakage (more sweating than leakage) around the rear 
differential seals but the diff oil wouldn't be bright yellow would it?

I though maybe it was antifreeze but the car is using Audi G12 
antifreeze that is pinkish/reddish and definitely not yellow let alone 
bright yellow.  Brake fluid is not leaking since the reservoir is right 
at the top and it is definitely not bright yellow.

There is no smell of antifreeze or gasoline.

What ideas of what it can it be?

Thanks.

Peter