What is this green stuff dripping from 05 Impala?

This has got me stumped. A few days ago I noticed a spot of green on the driveway under the front of my wife's Impala. Seems a little TOO bright and green to be antifreeze--but I verified the car has red Dexcool in the radiator and overflow bottle. Fluid has no odor or taste, isn't sticky, feels a little oily like antifreeze--but again it doesn't belong. This drip has persisted for several days even though the car has been driven in the rain. I've looked under the hood and can't see any sign of it except for a barely-visible amount in the cross-member the radiator sits in. She swears she didn't hit a can of paint, a martian, a zombie, a vulcan, etc. She & I are both MSU Spartans and bleed green--but our vehicles haven't expressed a school preference. Any other logical explanation for it? Attachment 43328 (http://www.doityourself.com/forum/attachments/passenger-cars-suv-service-repairs-no-trucks/43328-what-green-stuff-dripping-05-impala-greenstuff.jpg)