We all know that colors do change under different illumination; however, colors still remain relatively constant. While the color of someone’s blue shirt may appear slightly different indoors then it does outdoors, a person can still tell that the shirt is blue. Even with the changes in wavelengths of light from the sun and light from artificial light, color still remains fairly constant. Chromatic adaption, prolonged exposure to chromatic color, is one reason for the consistency. When you walk into a room with a bright light, your eyes adapt and become less sensitive to the rich light. Memory also helps with color constancy. A person’s knowledge of the usual colors of things in the environment allows them to perceive things with richer color. Objects such as a red stop sign or a green tree may seem richer in color than unknown objects.
I found this color illusion on youtube. If you continue to stare at the dot in the middle of the screen, the castle appears to be in color. If take your eyes off the dot at any point, you will see that the castle is actually still in black and white.