In reality the Queen and Princess Margaret were almost the same height. Whilst Claire Foy is of similar height to the Queen, Vanessa Kirby (Princess Margaret) is almost 4 inches taller. In a scene of them walking together, Kirby has flat shoes to offset the height difference.
Throughout the series, various vehicles are seen to enter Buckingham Palace from the Mall entrance, where it can be seen that the road outside and inner courtyard are covered by black tarmac.
However, since the 1950's at least, the surface of the Mall and courtyard have actually been coloured red, using a synthetic iron oxide pigment.
However, since the 1950's at least, the surface of the Mall and courtyard have actually been coloured red, using a synthetic iron oxide pigment.