Which tertiary colour is formed when more yellow is added to orange?

Correct answer: Yellow-orange

The governing concept is how changing the proportion of a neighbouring colour shifts a tertiary mixture. Orange already contains red and yellow; adding more yellow makes the mixture lean toward yellow, producing yellow-orange. Therefore option A is correct. Red-orange would result from stronger red influence, while yellow-green and blue-green require green combined with yellow or blue, not orange with extra yellow. The answer depends on identifying both the mixture and its direction of shift.