We know the shape of a thing when we see it, but its shape will not be seen if it has no color. The color of a thing will not be seen if there is no light. So the color for us to see has to depend on light, just as the day on the sun; or the night on the moon and stars, and fire. When the light is strong, the color becomes apparent; and when the light is dim, the color becomes obscure. A thing shows its shape by its color: it is conspicuous when its color is deep; it is invisible when its color is light. There will be a striking contrast if the colors of the things are quite different while their existence will not be felt if their colors are almost the same.