https://news.cornell.edu/stories/2012/06/researchers-identify-gene-controls-tomato-ripening

This gene also influences how tomato fruit ripen, the reason commercial tomatoes develop into perfectly red, store-ready fruit.

However, this same trait reduces sugars and nutrients in the fruit.

Naturally, tomatoes unevenly ripen, showing darker green patches when unripe and variable redness when ripe -- traits that still show up in garden-variety and heirloom breeds.

However, in the late 1920s, commercial breeders stumbled across a natural mutation that caused tomatoes to ripen uniformly -- from an even shade of light green to an even shade of red.

The uniform redness makes it ideal for groceries, where customers expect evenly colored, red fruit.