A few plants have non-green leaves throughout the summer, however. In this case, chlorophyll is present and functional in the leaves throughout the summer, but as each leaf ages, another type of plant pigment known as an anthocyanin begins to accumulate, tinting the normal green to a red-purple. Anthocyanins pigments range in colour from red to blue, and are responsible for most plant parts that are coloured red blue and purple. In a large number of plants, the level of anthocyanins tend to build if the plants are exposed to bright light when the temperatures are low. This is also why we see an increaseing reddening of some plants in fall.
Carotenoids are the third major type of plant pigments.
These pigments normally range in colour from yellow and orange to red. It's easy to remember the name of these orange pigments once you know that they were first identified as the colouring agents in carrots. Yellow carotenoid pigments are present in most leaves during summer, but because chlorophyll is also present at this time, their yellow colour is concealed. When a plant suffers from a lack of nitrogen, however, the level of chlorophyll decreases, and the yellow colour of the carotenoid pigments become more obvious. Very often, when a plant turns yellow, it is because the chlorophyll level has decreased, and the carotenoid pigments have simply become more obvious.