Why the difference in hospital uniforms

[sandyford]

In the picture of 4 soldiers, which is hopefully attached, taken in 4th General Hospital, Lincoln, 1915, the hospital uniforms differ in colour.

My father is on this picture and so far as I am aware there were no other Northumberland Fusiliers in with him.

Does anyone know why soldiers in the same hospital in England would wear uniforms differing from each other? Were these uniforms centrally issued, issued by the hospital or what.?

Or perhaps 2 had been washed with a powder that removed those unmentionable stains.

Kate C.