In the dark undergrowth of forest the amount of light that penetrates to the ground is about 2-3% of this what is over the top of the canopy. Many plants living or starting life on the ground developed very sensitive green receptors (chlorophyll) to catch all the dimmed light (dispersed photons). The just opening leaves have very sensitive structure and are very vulnerable to damaging, in case if a direct beam of sunlight breaks through and hits the leaves. For this reason, some young opening leaves protect themselves using chemical compound, a filter called anthocyanin that gives the reddish tint. Another tactic is the vertical position of the bad and leaves that limits the effect of direct noon light.