Where does the gene for green color come from?

[Vatsal Goyal]

I was studying evolution and speciation and an example was given in my textbook. It said that there is a species of red beetles and through variation a green beetle is formed and then is naturally selected as red beetles are easily seen by crows and green are not. My question is where does the gene for green color come from?

For variation to take place, shuffling of genes takes place in sexual reproduction but for which there has to be a gene for green color according to me.

 

[DrClaude]

Mutations are random.