It takes three things to see color—our eyes, light, and objects—and all three are variable.
Changes in the human eye: Genetics, color memory, eye fatigue, color blindness, and medications are just some of the variables that affect our ability to distinguish between color differences. Plus, we've all seen a bit of a difference in the colors, which led to a split between operators and shifts.
Changes in the type of light: Light has the biggest effect on the colors we see. The visible spectrum, also known as the rainbow (RGBIV), contains light with wavelengths around 400 to 700 nanometers and is broken down into three primary colors: red, green, and blue. Each type of light, such as incandescent, fluorescent, and daylight, has a different combination of wavelengths and therefore emits a different type of light.
Reflection of an object: The object itself has no color. Their properties determine which wavelengths of light are absorbed and which are reflected. It is a mixture of reflected light entering our eyes, giving us perception of color. When the type of light changes, such as between fluorescent lamps in a factory and daylight, the amount of light reflected by objects -- and the resulting color -- also changes.