Which habit is useful for filling a background with an even colour?

Correct answer: Reload the brush with the same mixture

Using the same prepared mixture each time the brush is reloaded helps maintain a consistent hue, value and concentration across the background. Therefore, option A is correct. Changing the colour at every stroke creates visible variation, a completely dry brush may leave rough or incomplete marks, and folding the paper does not control the paint layer. Preparing enough matching mixture also reduces patchiness.