What would have happened if plants lacked anthocyanins?

Anthocyanins are flavonoid compounds in the phenolic group and are composed of anthocyanidin aglycone plus one or more mono- or oligosaccharide units held together by glycosidic bonds. These water-soluble, vacuolar pigments are synthesized through the phenylpropanoid pathway and may appear red, purple, or blue based on pH-dependent structural changes. They are found in the cell vacuole in flowers and fruits and can also be found in the epidermis and peripheral mesophyll cells in leaves, stems, and roots. Anthocyanins are abundant in food plants such as blueberries, raspberries, grapes, and black soybeans.
These compounds provide physiological benefits to the plant and also function in plant/animal interactions, making them critically important to the plant's survival. Physiologically, anthocyanins function to protect the plant against extreme temperatures and also have antiviral, antibacterial, and fungicidal properties. The light absorbance pattern of these pigments is complementary to that of green chlorophyll pigments; therefore anthocyanins have the potential to mitigate photo-oxidative injury in photosynthetically-active tissues, such as leaves. This is accomplished by shielding chloroplasts from high-energy radiation and reducing reactive oxygen species.
The bright colors produced by anthocyanins may also function as aposematism defense mechanisms, visually discouraging potential predators from consuming the plant. Further, anthocyanin-based colorization may help certain plants camouflage themselves by mimicking dead or aging foliage. Beyond defense, this colorization also helps attract pollinators and seed-dispersing frugivores to the plant, thus increasing reproductive success.
https://www.researchgate.net/publication/226354956_Role_of_Anthocyanins_in_Plant_Defence