THE CHANGING OF THE GUARD, ST. JAMES'S PALACE.
From time immemorial there has been an interesting ceremony daily at St. James's Palace from 10.45 to 11 a.m., when the Guard is changed. Either the Grenadier or the Coldstream or the Scots Guards parade, to the music of their band, while the incoming commandant is supposed to receive the keys of the Palace; the officers marching to and fro, as shown in our view, carrying the standards of their regiments. Until 1862 when building operations were in progress, the ceremony took place in "Colour Court" (so called from this custom, but now it is observed in the Friary Court, the largest open space in the Palace. In this court, which overlooks the gardens of Marlborough House, is the entrance to the State apartments.
source: The Queen's London : a Pictorial and Descriptive Record of the Streets, Buildings, Parks and Scenery of the Great Metropolis, 1896