Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green ? Why?

Leaves on the shady side or from shade-grown plants are darker green because they contain a higher concentration of chlorophyll per unit leaf area

In low-light environments plants up-regulate chlorophyll synthesis to maximize light capture, increasing total pigment content and deepening green coloration

Shade leaves often develop thinner lamina and larger surface area, allowing more chloroplasts to be packed into a given area and enhancing light-harvesting efficiency

By contrast, sun leaves are thicker with more cell layers but lower chlorophyll density per layer, balancing light capture with protection against excess light damage

The dominant internal factor determining this difference is chlorophyll amount, which is higher in shade leaves to compensate for reduced light intensity