Which method is suitable for showing colour variation in natural leaves?

Correct answer: Use different values of yellow-green and blue-green

The governing concept is variation in hue and value. Natural leaves are not all identical, so combining yellow-green and blue-green, then changing their lightness and darkness, can suggest differences in species, lighting, age, and surface direction. Therefore, option B is correct. One uniform green removes variation, red is generally unrelated to the observed green structure, and black and white alone remove the useful colour differences. Controlled variation makes the foliage appear more natural.