Why can cases or words grow on Apple?

During festivals, we often buy red apples with yellow words on them, such as "Hi" and "Fu", and even some apples have all kinds of beautiful patterns! The calligraphy and painting on these apples can't be washed or erased because there is nothing written on them. So why do these patterns and words grow on apples? It turns out that the color of apple changes with its maturity. Growing apples are green because of chlorophyll. With the ripening of apples, changes in temperature and light, physiological and biochemical reactions have taken place inside apples, chlorophyll has been continuously decomposed and disappeared, and anthocyanins have been continuously formed, making mature apples appear red. People skillfully make artistic apples by using the color-changing characteristics of apples. Usually, when the apple matures and grows to a certain size, use a piece of opaque black paper with good texture to carefully cut out the patterns or characters you like and cover it on the sunny side of the apple for shading. After the apple is ripe, the part covered by paper-cut can't be used for photosynthesis, so the sugar content is low and the lack of light affects the formation of anthocyanins. This part of the color change is only the disappearance of chlorophyll, accompanied by the appearance of carotene, so it appears yellow. After sufficient light, the sugar of photosynthetic products accumulated continuously, and the original green color was gradually replaced by red color containing anthocyanins. Finally, Apple put on "red clothes". In this way, after tearing off the black paper, a calligraphy and painting with obvious contrast between red and yellow is formed on the surface of the apple.