In which direction will yellow shift when a little red is added?

Correct answer: Toward orange

On the traditional colour wheel, yellow and red are neighbouring primary colours whose mixture produces orange. Therefore, adding a small amount of red to yellow shifts the hue toward orange, making option D correct. Yellow would move toward green if blue were added. It would not move toward blue or violet, because those hues are not the immediate direction created by adding red to yellow; the exact shift depends on the amount added.