There are a ton of theories out there. It depends on a whole bunch of factors – the environment conditions, which animals eat it, if it’s been genetically modified/bred to have certain color characteristics, etc.
Some fruits are red to attract animals so that they can disperse the seeds after being eaten. Birds are hella into red, for example. That said, most animals don’t see things how we see them.
Some fruit/plants are able to limit sun damage by reflecting a specific UV wavelength which in turn may give the fruit a red color in visible light.
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