We had our drive block paved last summer and are happy with the result,
no sagging or other problems as far as I can see. But over the last few
weeks of damp weather the drive has taken on a distinctly green hue,
less so where the cars are normally parked. What is this? Is it moss or
mildew or something similar growing in the surface of the blocks due to
being damp all the time? What can I do to clean it off and stop it
coming back?

Any ideas welcome.
TIA
Andy