It's a work of art. Or, if you rather, a clock.
It's pretty simple. The time of day sets the colour, while the minute sets the lightness (bright on the hour, becoming dim) and the second sets the saturation (saturated on the minute, becoming dull).
If you get really good, you can probably tell the approximate time from the colour alone. Good luck!
You can set a time zone by adding a #TimezoneName to the URL. Try #UTC or #Canada/Eastern