It is well known that the ‘usual’ green colour is due to the presence of chlorophyll in the leaves, which harvest red and blue light to fuel photosynthetic reactions. In turn, photosynthesis allows the plant to produce carbohydrates (sugars) to sustain growth and development, together with converting carbon dioxide into oxygen. When temperatures start to decrease, and days to shorten, the amount of chlorophyll in the leaves slowly decays. Indeed, warm temperatures are required for the plant to replace the chlorophyll which is gradually decomposed over time. As the concentration of chlorophyll decreases, other dye molecules present in the leaves become more and more visible. These are essentially carotene (which gives carrots their colour) and anthocyanins (present in red grapes and wine). Depending on the tree, and on the weather conditions, the leaves become yellow or more red-brown as the green colour fades, giving rise to awesome landscapes. I spent some holiday in Japan just one year ago, and the weather forecast during this period includes very detailed maps showing the ‘red leaves forecast’!

Autumn colors in Japan, here in Shirakawa-go....

... and in Nikko.

And here are some of the molecules responsible for these various and impressive color changes: