What is most useful to record for recreating the same mixed colour?

Correct answer: Proportion of the mixed colours

The governing concept is reproducibility in colour mixing. The final appearance of a mixed colour depends greatly on which colours were used and how much of each was added. Recording a ratio, such as two parts yellow to one part blue, gives a practical guide for repeating the mixture. Thus option D is correct. Brush size, paper length, and the painting’s name do not specify the mixture itself.