A wild plant displaying red, green and yellow colour leaves, clicked at the Hyderabad Collective, Bodakonda, Telangana.

Leaves are ‘food factories’ of trees. They use 3 ingredients – Sunshine, water and carbon dioxide and cook up food for the entire plant through the scientific process of photosynthesis. An essential element of the leaf which enables photosynthesis is a pigment called chlorophyll – which you all know is also responsible for giving a leaf its amazing green colour. However, we also find leaves of varying shades of green, leaves that are naturally pink, red or brown, and leaves that change their colours throughout the year and their lifetime. So, what exactly is it that gives leaves their colour? And what can we infer from the colours of the leaves? Let’s find out.

Why are Leaves Green in Colour?

The concept of colours is quite ‘spectacular’. We see colours as a result of the wavelengths that are reflected back to our eyes. Molecules of various elements in the world naturally absorb certain wavelengths from the electromagnetic spectrum of colours & reflect the others – the reflected ones being the colours we identify the elements with.

As you already know, leaves get their green colour from Chlorophyll, which is crucial for photosynthesis. It is the process by which plants and some other organisms convert light energy, typically from the sun, into chemical energy in the form of glucose. So, the Chlorophyll molecules in the chloroplasts of plant cells absorb light energy from the sun, primarily in the blue and red regions of the electromagnetic spectrum, but do not absorb light in the green region as effectively. Instead, they reflect and transmit green light. This is why we perceive leaves as green.

The absorbed light energy is used to power a complex series of chemical reactions that convert carbon dioxide and water into glucose and oxygen – giving us humans the element of life. This energy conversion is not just important for leaves but is also the foundation of the food chain and is essential for the growth and survival of most living organisms on Earth, including humans.

Are All Leaves the Same Amount of Green?

The greenness of leaves can vary based on several factors. Chlorophyll – the predominant pigment in the leaves, is of 2 types – chlorophyll-a (blue-green) & chlorophyll-b (yellow-green). The ratio of these two chlorophyll types in a leaf can influence its shade of green. Leaves with a higher concentration of chlorophyll-a will appear bluish-green, while those with more chlorophyll-b will appear more yellowish-green.

In addition, the overall amount of chlorophyll in a leaf itself can vary. Leaves with a high chlorophyll content will appear darker green, while those with lower chlorophyll levels will appear lighter green. Young, newly formed leaves often have higher chlorophyll levels, as they need more food to grow, and are typically a brighter green. As leaves mature, chlorophyll levels may decrease, and other pigments become more visible, leading to changes in leaf colour. Furthermore, different species of plants have varied levels of chlorophyll, giving them naturally dark or light green colours. Even on the same plant, you can find variations in the greenness of leaves. This can be due to genetic differences, variations in light exposure, and other factors.

As the green colour of leaves relates closely to the food-producing process (photosynthesis), the amount of nutrition & overall health of the plant can showcase different colours in leaves. Well-nourished and healthy plants typically have more vibrant green leaves, while stressed or nutrient-deficient plants may have paler or yellowing leaves. This is closely related to the environmental conditions, such as light intensity, temperature, and water availability, which can influence the greenness of leaves. Plants in low-light conditions might have darker green leaves to capture more light, while those in very bright conditions might have lighter green leaves. This is why you may find indoor plants typically displaying dark leaves, while deciduous plants that are exposed to a lot of sun display lighter shades.

But leaves do display colours more than green, which brings us to our next section – what other pigments are present in a leaf besides chlorophyll, and what role do they have to play?

Leaf Pigments & Their Roles

There are four primary types of pigments present in leaves.

Chlorophyll: While the function and importance of this pigment have already been established, it is important to know that Chlorophyll is also the most abundant pigment in a leaf – the reason why most leaves appear green.

Carotenoids: A group of pigments found in leaves which is responsible for a range of colours, including yellow, orange, and red. Carotenoids help capture light energy and protect the plant from excess light damage. Common carotenoids include beta-carotene (orange), lutein (yellow), and zeaxanthin (yellow).

Anthocyanins: They are responsible for the red, purple, and blue colours in many plants, including some leaves. These pigments are not always present in leaves but can be produced under certain conditions, such as exposure to cool temperatures in the fall. They act as antioxidants and can help protect leaves from damage.

Flavonoids: They are a diverse group of pigments that can contribute to various leaf colors, including red, blue, and purple. They serve multiple functions in plants, including UV protection, pollinator attraction, and defence against herbivores.

These pigments work together to give leaves their characteristic colours, and their presence and concentration can change based on factors like the plant species, environmental conditions, and the plant’s stage of development. But the most common and striking changes in a leaf’s colour can be seen during a seasonal change. Let’s dive deeper into how that happens.

Why do Leaves Change Colour?

Leaves change colour with the seasons due to a combination of environmental factors and chemical processes within the leaves.

As the seasons change from summer to fall, the amount of daylight decreases, and temperatures drop. This change in environmental conditions signals to the trees that it’s time to prepare for winter. During the spring and summer, leaves are green because of a pigment called chlorophyll. However, as days shorten and temperatures cool in the fall, chlorophyll production slows down and eventually stops.

When chlorophyll production decreases, the green colour fades away. Here’s where the other pigments, that were present in the leaves all along, take the spotlight.

Carotenoids are always present in the leaf, but they are usually masked by the dominant green chlorophyll. When the green chlorophyll breaks down, the yellow and orange carotenoids become more visible, resulting in the warm, golden colours of many autumn leaves. In certain tree species, like maples and some oaks, cool temperatures trigger the production of anthocyanin pigments. These pigments create vibrant red and purple hues in the leaves.

This transformation of leaves is a remarkable and beautiful adaptation that helps trees prepare for the winter months.

Can Leaves Naturally Be ‘Not Green’?

Yes, leaves can naturally be of colours different from green throughout their lifespans. While green is the most common colour for leaves due to the presence of chlorophyll, many factors can cause leaves to exhibit colours other than green. 

Some plant species naturally have leaves that are not green. For example, certain succulents like Echeveria have blue, grey, or pinkish leaves due to specialised pigments and structural adaptations that help them survive in arid conditions. To add to this, within a single plant species, there can be genetic variability that results in different leaf colours. This can include variations in shades of green, as well as leaves with natural variegation (stripes or patches of different colours). Furthermore, plants and trees present in perpetually cold environmental conditions, such as maples and oaks produce anthocyanin pigments that give leaves red or purple hues.

Leaves are some of the most common yet fascinating elements of the natural world, and their colourful disposition tells us a great deal about their condition. Next time you spot a particularly vibrant green leaf, or a uniquely coloured one, hope you reflect upon the subsurface elements that have filled the world with a little more colour.