According to Genesis, a rainbow appeared in the clouds as the sign of God’s covenant after the Flood.
Genesis 9:12–17 presents the rainbow as a visible reminder of the covenant between God, Noah, every living creature, and the earth. The passage says that whenever the rainbow appears in the clouds, God will remember the covenant and will not again destroy all life with a flood.
The rainbow therefore functions in the story as a covenant sign, not merely as a description of weather. The text places this promise after Noah leaves the Ark and builds an altar. In modern usage, rainbow imagery has acquired many additional associations, but the Genesis account’s specific connection is the post-Flood covenant.