What is The Process of Fruit Ripening and Change of Color     from Green to Yellow or Orange  ?

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Several Major  change can take place as fruits ripen not all occur in every type of fruit, but taken collectively they characterize ripening processes they include (1) a rise in respiration rate (2) production of ethylene (3) flesh softening (4)appearance of color (5) formation of volatiles with associated development of flavor.

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Among these changes formation of bright colors, which evolved to attract dispersal agents such as birds, browsing animals, and primates, now become a particularly important visible indicator of maturity and ripeness pour fruit, stone fruit , tomatoes, mangoes and straw berries provide good examples where color is a prime indicator of ripeness. The non greening of leaves its called senescence as in leaf denescence, ripening in fruits also involves chlorophyll loss and an increase in production of yellow, orange, red or purple pigments,.Yellow, orange or red pigmentation  as seen in oranges and tomatoes, arise from convesion of chloroplasts to chromoplasts. In higher plants, carotenoids which are found in chromoplasts. and anthocy units which are located in the vacuoles fulfill an important purpose as colorant of fruits. 

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For example the red color of tomato (lycopersicon esculentum) fruits is due to the carotenoid pigment lycopene, whose concentration increases dramatically during the ripening process. the deep yellow colour of mango fruits is duo to the presence of beta carotene a common phytochemical within a group of 600 known carotenoids. similarly the red colour development in apples and purple colour development in grapes are due to the formation of anthocyanin pigments in their skin. sometimes both types of pigments can occur in the same fruit. these  pigments are formed as end products of too separate pathoays during ripening the pathway, which leads to the accumulation of yellow - arange carotenoids or red lycopene and the anthocyaning pathway which leads to the accumulation of anthocyanins in the vacuoles are these two pathways. 

source :- THE HINDU