Why are red, yellow, and blue considered primary colours in traditional painting?

Correct answer: Because many other colours can be made from them

The governing concept is the traditional RYB model of paint mixing. Red, yellow, and blue are called primary because they are treated as basic starting hues from which many secondary and further mixed colours can be produced; for example, red and yellow make orange. Option A is correct. They are not all simply warm, their lightness can vary, and their use is not limited to posters. Modern printing and digital systems may use different models, but the question specifies traditional painting.