The blue, yellow and red plane colours are explained in the Photoshop Help, but green isn't mentioned, as far as I see.
When you Opt/Alt-click the stamp tool inside a plane, that plane turns green to indicate that it is the source plane for the perspective transformation that's applied when painting with the stamp.
What exactly do you mean by "clone does not work". Screenshots tend to help, too.
UH OH, I had a hidden selection active.
My bad, thanks for help! But what do
the other grid colors mean?
Like I said, the colours other than green are explained in the help. There's a big page about Vanishing Point.