This incredibly detailed colour scheme is remarkable. It can be seen that Elliott was using 21 colours - see abbreviations at top. The colours had to contrast and harmonise simultaneously - incredible mastery for a 23 year old. His mastery of colour, composition and spatial relationships are extraordinary. The red dots at top right were used to note observed flaws in the masterpiece. These were then worked on and the dots removed. Such a system was necessitated by the nature and complexity of the piece. It was impossibile to retouch at the time. Digital retouching arrived as a high end option in the late Eighties, Photoshop in 1990. Transparency retouching on small format - essential for the depth of field - was impossible. So the masterpiece is unretouched.