What would have happened ? If.............

Plants lacked anthocyanin.

Anthocyanins are plant pigments that may appear red, purple or blue depending upon their pH. Fruits like blueberry, black rice, raspberry are rich in anthocyanin. Till now their basic function known is to impart the attractive colors to the plants, other functions of this pigment are known. There is also no evidence that anthocyanins have any effect on human biology or diseases. So, if they would be absent, plants possessing them will become colourless.