While some Christians have used the colors of the rainbow in interpreting or usurping meaning from the biblical stories, the Bible itself assigns no meaning to the colors. The rainbow appears only twice in the Bible, in the first and last books. Christians feel its first appearance in the story of the flood is special, because the biblical flood story is the only one that features a rainbow. God places a rainbow in the sky as a symbol that the rains have ended and that a flood of such proportions will never come again.
Christian theories about further meaning to the rainbow and its colors primarily center on attempts to present a correlation between the seven colors of the rainbow and the seven days of creation. The rainbow has also been used to draw parallels to light, as God's first creation, and all of the colors of the earth, as reflections in various combination of the colors represented in the rainbow. Graduated further, the point becomes that God gave man light to show us that he encompasses all things. For this same reason, the rainbow is sometimes used as a symbol of Jesus, through whom Christians believe all things are possible.
In the Bible, the color red typically stands for sin and the blood of Christ that offers redemption. The Bible also discusses red as a color of suffering in the books of Exodus and Isaiah. By contrast, the color orange represents judgment upon human actions, as Biblical authors discuss in both the books of Psalms and Revelation. Pottery in the Bible is often orange, and Biblical characters occasionally smash pottery to express their disgust at human behavior.
The color yellow stands for eternal life and glory. In many points in the Bible, a yellow glow signifies Godliness and spiritual status. In addition, in the book of Job, the color yellow stands for bitterness.
Purple in the Bible stands for royalty. Kings in the Bible often dressed in the color. In addition, high priests of the Bible used the color purple for the Gate of the Tabernacle. In the Bible, purple often stands for God's justice and His plan to bring justice upon the world.
As a whole, God displays the colors of the rainbow at the end of the flood that destroyed the world. The colors combined stand for the power of God, according to the book of Ezekiel. When God shows the rainbow to Noah after the flood, it is His sign that God's plan is to never again destroy the world with a flood.