I like how nature can grab my attention with color. It does not have to be a brilliant color but one that pops out within the frame. There are many reasons leaves will turn yellow. One is a lack of adequate light. When plants become shaded by other plants or by branches higher up on the same plant, the chlorophyll fades away and the leaves yellow. They also change colors because they are not able to maintain adequate levels of the green pigment, chlorophyll. For me it does not matter as long as I enjoy the beauty it presents.