Which colour may commonly appear between blue and yellow when they are blended directly?

Correct answer: Green

The governing concept is subtractive colour mixing used in common paint practice. Blue and yellow pigments generally produce green, and a direct transition between them may visibly pass through green shades. Thus option D is correct. Orange is associated with red and yellow, purple with red and blue, and red is not the usual result of mixing blue with yellow. Exact results can vary with pigments, but green is the standard school-level answer.