Reading the official report the female pilot stated visual conditions were not great with rainwater beading on the side windows. Fair enough I suppose, she also stated she was unsure if the other helicopters rotor was rotating, again I thought under those weather conditions it would be difficult to spot a rotor aligned front to back.
Until the actual impact. Then I could see the parked heli's rotor (as it fell off) had white strips. Not sure how she missed the spinning rotor with those white markings.