What is the meaning of a metaphor 'i am a rainbow'?

In the book of Genesis chapter 9 God gives Noah a promise that He will never again flood the earth to kill every living thing. He told Noah that He was placing a rainbow in the clouds as His permanent promise that He would never again kill everything with a flood. Gen 9:8-15 KJV And God spake unto Noah, and to his sons with him, saying, [v. 9] And I, behold, I establish my covenant with you, and with your seed after you; [v. 10] And with every living creature that is with you, of the fowl, of the cattle, and of every beast of the earth with you; from all that go out of the ark, to every beast of the earth. [v. 11] And I will establish my covenant with you; neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth. [v. 12] And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations: [v. 13] I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth. [v. 14] And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud: [v. 15] And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh.