If a painting shows a gradual transition from red-orange to yellow-orange, which quality does it demonstrate?

Correct answer: Colour harmony and gradation

The governing art concept is colour gradation within a related colour family. Red-orange and yellow-orange are neighbouring tertiary hues that share orange and can shift smoothly from one to the other. Their closeness creates harmony, while the gradual change demonstrates gradation rather than sharp contrast. Therefore A is correct; B concerns shape, C means absence of colour emphasis, and D requires black and white.