Question

Why do most leaves have upper surface more green and shiny than the lower one

Answer 1

this is because the upper layer is the one that is exposed to light (sunlight).
☆photosynthesis is a process that requires both chlorophyll and sunlight (including water and co2) and since the upper layer of the leaf is exposed to more direct sunlight than its lower layer,the upper layer of the leaf has more chlorophyll , so that it can trap the sunlight and convert it into chemical energy for photosynthesis
☆in addition the upper layer of the leaf is also shinier than the lower layer because it's covered with cuticle ,which reduces the rate of transpiration (which is usually more from the upper part of the leaf than the lower part because it is the one that is correctly exposed to sunlight which increase the rate of evaporation i.e. transpiration)