In late December, right before marijuana made its loud and proud entrance into the Colorado retail economy, I walked down to Civic Center Park to see if you could still buy a nickel bag off a stranger, as I did when I first moved to town a decade ago. I was not surprised to find that you could — and was equally unshocked last week when I returned to the park and found the black market just as busy…if not more so. There were a few key differences between my pot purchase in Civic Center in late December and my post-legalization trip there last week, though.