Have you seen a tomato before it is ripe? It is green, sour and not very soft. However, as time passes, it changes its colour: first into yellow and then red. Most fruits are green in colour before they ripen. They may not be sweet and delicious as they would be when they are ripe.
Nature is playing a trick here. The unripe fruits do not contain mature seeds. Therefore, they need protection from animals and birds until they are ripe. These fruits are hidden among green leaves so that they escape the notice of others. When they ripen, they start attracting animals and birds, in turn, will be carries and disperses of seeds.
Picture Credit : Google