Why upper surface of leaves is more green and shiny than the lower one?
You can find two chlorophylls in most plant leaves, chlorophyll a and b. We'll use as a reference Leaf characteristics and chlorophyll concentration of Schyzolobium
parahybum and Hymenaea stilbocarpa seedlings grown in different
light regimes. The most important observation is that in shade-tolerant leaves, chlorophyll b dominates chlorophyll a. And the opposite is true of shade-intolerant leaves. I'll argue now that the portion of a given leaf that must tolerate more shade will have the darker green pigment due to the presence of more cholorphyll b, and that the side of the leaf that must tolerate lots of light will have the lighter pigment due to the presence of more chlorophyll a.

The light-tolerant side of the leaf is also shiny, and this is because of a thick waxy cuticle. The shade-tolerant side of the leaf also has a cuticle but if we follow it logically, the light-tolerant side of the leaf needs more protection from heat evaporation because it's always being hit by light.

So what I'd do, instead of thinking of the leaf as having a top or bottom, think of them as having a side that must tolerate excessive shade, and a side that must tolerate excessive light.