The "Background" link in the top menu bar of this site allows you to select a preferred background color for the pages viewed in one visit. You may, or may not, have noticed that the second background gradient is made from the inverted colors of the first background. In the same way, the fourth background gradient in made from the inverted colors of the third background.
Of course, when inverting the colors of the second and fourth backgrounds, you get back the original colors.
When inverting colors of the water element, you get the colors of the opposite element, fire; the contrary also works. When inverting the colors of the earth element, you get the colors of the opposite element, air; again the contrary also works.
Cyan is the universal swimming pool color and blue is the color of water. Red and yellow are the colors of the fire. Black and brown are the colors of soil while white and light blue are the colors of clouds and sky.