Once a large-scale rainbow appeared before me so that I could learn from it what rainbows are like at the smallest scale. There was a brilliant white light with a kind of belt about it. At the core of the belt was something dim and earthlike surrounded by a bright radiance. The radiance was dappled and broken up by another kind of light containing golden starlike sparkles. Other changes occurred when flowers of different colors entered into the bright radiance—colors produced not by white light but by a fiery kind of light. All of it represented heavenly and spiritual qualities.
In the other world, all visible colors represent something heavenly or spiritual. Colors that partake of fire represent aspects of love and of a desire for what is good. Colors that partake of white light represent aspects of faith and of a desire for truth. All colors in the next life come from these sources and therefore gleam so brilliantly that colors in this world cannot be compared to them. There are also colors that have never been seen in the world.
from Secrets of Heaven, Volume 2, Section 1624