Piles of bugs

We've been seeing these things in little clusters near paving stones for the last few weeks. At first we thought somehow paint had spilled, but up close it's a mass of tiny jumping insects, like fleas. Up close, you can hear a noise like rain that's the jumping on the leaves.
Even in the water dish:

It seems they're Springtails, maybe the version called Snow Fleas. In most descriptions they're not purple but I have seen some photos resembling ours (also blue, white, pink and black). Strange things. For descriptions: What's that bug?; Cold weather acrobats.