What is the best way to keep the same mixed colour uniform over a large area?

Correct answer: Prepare enough paint at one time

Uniform colour depends on keeping the proportions of pigment, binder, and water as consistent as possible. Preparing enough of the required mixture in one batch means the same ratio can be used across the entire large area, making option A correct. Mixing a new batch for each section or adding different amounts of water can produce visible shade and opacity changes; applying unmixed paint does not solve the problem.