[1] During the First World War he gave up part of his house for an extension to the Ethel McCaul Hospital in Welbeck Street, London, which with his encouragement used colour therapy to treat victims of shell shock (PTSD).

By the second year of the First World War, with so many families losing their young men, interest was growing in spiritualism and theosophy, notably involving Rudyard Kipling and Bibby's Magazine.

In 1916, Prossor put to the test his theories of how colour could affect the psyche with a Peace Room in a house in Chelsea which was the subject of a report in The Times.

The paper said the Peace Room scheme was complemented by recitals of "symbolic music" by Irene Penso and Georges de Warfaaz and was "evidently inspired by aestheticism and esoteric beliefs".

[4] In 1916, Prossor's theories were attracting international attention and Algemeen Handlsblad noted him as "the greatest and most famous decorator in London".

It goes on: “Imagine the change of being transported from the tortured battle-grounds of Europe, desolate, and reeking with the carnage of war, to these wards where ‘all the air is thrilling with the Spring,’ for that is the message of Mr Prossor’s colour wards.” Flight magazine in 1918 praised the benefits of Prossor’s colour schemes for airmen with “nervous affections” after active service.

“Every other consideration apart, we simply cannot afford to ignore any method of treatment” A report in the Herald of Wales in 1918 is typical in the information it gives about the colours used by Prossor.

[9] In 1918 the Union of South Africa public works department proposed to adopt Prossor's colour schemes in all its mental wards,.

[10] In 1919, the Red Cross opened a hospital at Russell Lea, Sydney, Australia, with Roy de Maistre, a young artist, borrowing Prossor’s idea for the colour cure.