I agree with CSA on this one. I moved one of my cars yesterday and spotted a line of yellow drips on the snow where the car was parked. There are no fluids in my car that are yellow, and there were no animal tracks under the car. Considering I had recently returned from a long trip on the PA Turnpike, where they use LOTS of salt and other chemicals, I concluded it was the salt that made the yellow spots.
Even if your coolant is yellow, how would it drip from the rear wheel area?