Green Park Slope Paving Stones? It's Herbicide!

At first, we thought the paving stones on Prospect Park West had suddenly gone green due to the weather and that everything had started looking a little like the English countryside spring, a bit mossy and green. Then we saw the signs posted for the herbicides that have been sprayed. Nothing overly nasty, of course, just stuff that irritates skin if absorbed, can harm aquatic life, etc.