What is the greatest advantage of writing proportions beside each mixture in a colour chart?

Correct answer: It becomes easier to reproduce the mixture accurately

The governing concept is recording and reproducing a colour formula. If a chart notes proportions, such as two parts yellow to one part blue, the artist can repeat the same relationship instead of relying on memory or guesswork. This improves consistency when preparing a larger quantity or correcting a later section. Recording proportions does not make the paper heavy or thick and does not itself increase brightness, so option C is the only relevant advantage.