Neon colored leak in rear of vehicle on 2005 Chevrolet Uplander

I have something neon colored leaking under rear end of my Uplander. Any suggestions of what this could be?

You have both antifreeze and R-134 going to the rear heat/cooling unit. The R-134 will have a neon colored leak detector in it. Or if the antifreeze is not the original DexCool, it could be green color also. The leakwould be on the driver's side, just behind the rear wheel.