Whenever a new Pope is elected a quick renovation of the papal apartments is carried out. In 1963 the Archbishop of Milan was elected and so he hired Milanese designers to fit the apartment to his tastes.
It was then that the lovely, vividly red crimson damask came off the walls and in its place they put up this more "humble" looking brown (which never matched the Baroque ceilings or floors). Forty years later Pope John Paul II had the brown taken down and new damask put up, albeit this time a lovely white with the pattern of festoons and tiara with keys.
So now that the Apostolic Palace of the Vatican and the Papal Summer Villa at Castel Gandolfo are done, now someone just needs to remind them that now they have to save the walls of the Lateran Palace from this same (brown!) wall-covering!