Zerex G05 is dyed yellow.
And agree that it's probably HVAC condensate for you, Taenianotus. When it drains, it runs down the frame, picking up all kinds of oils and glycols thrown up from the road. If the drip pan's not brand new, the water will also mix with any oils on its surface. Voila, oily clear spot at the rear of the engine.
IronHorse55, unscented and clear is throwing me. The only truly clear fluids on the vehicle are power steering fluid (which could be leaking there—the cooler's mounted in front of the radiator) and brake fluid, both of which have a very distinct hydraulic fluid smell. The dyes in the coolant are normally visible in even in small quantities, and it's got a pretty typical coolant smell.
Either way, as was said, you're definitely due for new coolant on an '06 if it hasn't been done; it's 5 years (i.e. 2010 on most '06es) or
100K miles. Won't hurt to swap it out or do the hoses if they look questionable. Worst case you have fresh coolant and still have a mystery fluid.