You are talking to a blind man who asks you to describe something with the colour "indigo". Write down what you would tell this man without once using the word "indigo" in your explanation. [I'm doing this for all 7 colours of the rainbow as a writing slump cheat. Read my green, yellow, orange, blue, red post.]
Ah, the colour of the night sky lit by starlight. Not quite complete darkness, not really bright either. Nothing quite captures intrigue and mystery like it does. It signals something greater and larger than ourselves. It's the closest colour to our sense of wonder. Sitting by the beach on a still moonless night, with only stars as light; seeing the galaxies and constellations far out into the sky; an occasional shooting star streaking across the sky; the sea like a mirror reflecting the everything above. Can you imagine that? Can you see yourself sitting there, wondering how huge this universe is, and what's our place in it? What infinitesimal role do we play in such infinite vastness? Sitting there, you can't help feel your smallness but yet by asking that question, feel connected to that infinity. Now that is wonder that this colour brings. A wonder laced with awe, tinged with delight.