How does color affect light absorption?
The more green the plant, the more it absorbs the light. That's why the rate of photosynthesis is higher in greener plants.
Green color is the color of chlorophyll and carotenoids, the light absorbing agent. The more there is these two things, the more it is gonna absorb the light.
Leaves has the chlorophyll and carotenoids in most quantities. That's why the look more greener and are the main center for the process of photosynthesis.