Well, Berlin had been bombed by the US Eighth Air Force, RAF Bomber Command for well over a year, followed by shelling from thousands of Soviet artillery pieces, so rubble was everywhere (look at wartime photos). And not just bricks, but wiring, plumbing, wooden joists, roof tiles, bits of furniture, random shredded sheet metal, and lots and lots of paper. And scatter lots of completely unrecognizable bits into it .
And if you've ever been to a building demolition, there is gray cement dust absolutely everywhere, so colors should be very unsaturated.