In him was life, and that life was the light of men. The light shines in the darkness, but the darkness has not understood it. John 1:4-5
I've got a whole other post in the works on why I think "understood" in vs. 5 is a whack translation that undercuts the potential power of the message. That's for later.
This morning, as I was coming out of that last, half-in, half-out, dream state we sometimes experience just before time to get up, my mind's eye saw a picture of Noah, an altar and a rainbow. It was brief but clear and quite real to me on into the morning hours. In the course of my regular activities, the ideas of the rainbow of Genesis 9 and the light of John 1 began working in tandem in my ruminations.
And God said, "This is the sign of the covenant I am making between Me and you and every living creature with you, a covenant for all future generations: I have placed My bow in the clouds, and it will be a sign of the covenant between Me and the earth." Genesis 9:12-13
In the first covenant recorded in scripture, God chose the revelation of the essence of visible light as the sign of His promise.
Fundamentally, light is a continuous spectrum of wavelengths which means there are an infinite number of colors in the universe. However, God created us with only three types of color receptors in our eyes. These receptors dictate which part of the light spectrum is visible to us. A rainbow is formed when droplets of water in the air act as prisms to refract light at various wavelengths. We can see red, orange, yellow, green, blue, indigo and violet. Put them all together, we see white. Take them all away, we see black.
The following statements appears in the Wikipedia article on rainbows: The most spectacular rainbow displays when half of the sky is still dark with draining clouds and the observer is at a spot with clear sky overhead. A rainbow does not actually exist at a particular location in the sky. It is, instead, an optical phenomenon whose apparent position depends on the observer's location and the position of the sun.
I'll let you draw your own devotional conclusions from those.