Which record is most useful for recreating the same mixed colour?

Correct answer: Proportion of colours

The governing concept is reproducibility in colour mixing. A colour mixture depends strongly on the identities and relative quantities of its pigments, so recording the ratio—such as two parts blue to one part yellow—provides a practical recipe for making the same shade again. Option B is therefore correct. Brush size, palette colour, and paper thickness may affect application or appearance, but they do not record the mixture formula itself.