Which colour cannot be made by mixing red and yellow because it is itself a primary colour?

Correct answer: Blue

The governing concept is primary-colour identity and mixing. In the traditional school colour model, red and yellow combine to produce orange; changing the proportions or adding white or darkening material may produce lighter or darker orange variations. Blue is itself a primary colour and is not produced by mixing red and yellow. Therefore option A is correct, while the three orange choices can be related to that mixture.