Here's why:

* Chlorophyll: Leaves contain a green pigment called chlorophyll. This pigment is essential for photosynthesis, the process by which plants convert sunlight into energy.

* Photosynthesis: During photosynthesis, chlorophyll absorbs sunlight, specifically red and blue wavelengths, and reflects green light. This is why we see leaves as green.

While other parts of the plant might have some chlorophyll (like stems or young fruits), the leaves are the primary site of photosynthesis and therefore the most prominent source of the green color.