It may look grey in daylight, but it accents the background with colorful signals at night.
- Cosmic background, which we do not perceive, constantly send signals from space. We do not see it, do not hear it, and do not feel it, but it is there, around us, through radiation of the galactics, stars, and planets. All of that inspire bedtime stories.
- Technology background: cars that buzz, make noise, signal, pollute, and leave the soot in the clouds.