If the amount of red is gradually increased in a red and yellow mixture what is the correct colour progression?

Correct answer: Yellow to yellow-orange to orange to red-orange

The governing concept is proportional pigment mixing on the warm side of the colour wheel. Starting with mostly yellow gives yellow; gradually adding red first produces yellow-orange, then a balanced orange, and finally red-orange as red becomes dominant. Therefore option A correctly follows the changing ratio. The other progressions require colours not produced by increasing red in a yellow mixture, so they do not represent the stated process.