Planetary Folklore just posted this fascinating optical illusion of the following image which appears to vanish right before your eyes. If you stare long enough at the center of this cloudy combination of soft pastel colors of pinks, oranges, yellows, and blues, it results in what is known as “color fatigue”. The reason the image disappears is due to the fact that the retina of the human eye holds two types of photoreceptor cells: rods and cones. Rods are sensitive to light and dark (the majority of the photoreceptor cells in each retina are rods — approximately 120 million cells), while cones are sensitive to red, green, and blue light and are responsible for color vision (approximately 6 million cone cells in each retina). When our eyes are exposed to a hue for a prolonged period, the rods & cones become fatigued. You might notice this if you are reading something on colored paper, and then look away—you often see the inverse, or complement, of the image. This occurrence can be advantageous if you are seeking the opposite, or contrast, of a color, but can be dismaying to a viewer if presented with prolonged exposure to colored screens or reading materials. The phenomenon works every single time I look at the image below, although I find it works fastest when I focus on the whitest areas in the center of the image.