The boarders can be seen in their bluecoat uniforms at the centre of the picture.
From the en.wikipedia.org
For a long time the school was a traditional bluecoat school.
From the en.wikipedia.org
Humphrey Chetham purchased the old College buildings after the Civil War, and endowed it as a bluecoat school.
From the en.wikipedia.org
His parents met when his salesman father played cornet in a bluecoat band for a party at the Duke of Westminsters'estate in Chester, where his mother was a ladies maid for the Dukes household.
From the en.wikipedia.org
More examples
A person dressed all in blue (as a soldier or sailor)
The bluecoat is a traditional style of dress code, usually used in some British private schools especially made for Christ's Hospital.
The Bluecoats Drum and Bugle Corps is a World Class (formerly Division I) drum and bugle corps based in Canton, Ohio, and founded in 1972; The Bluecoats are a member corps of Drum Corps International. ...
A traditional dress code at certain prestigious British schools; A soldier or officer in the Union army during the American Civil War; A policeman