Original: Also, as a result of chlorophyll's relationship to tannin, younger growth is greener and more vibrant in colour, while more developed leaves further down the plant have had their chlorophyll convert gradually into tannin, giving a more bitter flavour and duller brown-green colour profile.
Simplified: Younger growth is greener and stronger in colour, while more developed leaves further down the plant have had their chlorophyll changed gradually into tannin, which gives a more bitter flavour and duller brown-green colour.