Our Fickle Eyesight
Our perception of color is so subjective. This page on illusion and color perception has some really interesting examples of the effects of an overall image on a specific portion of an image. For example, the two middle squares in the image on the left are actually the same color, despite appearing otherwise. The fascinating thing is that the effect is accentuated the more colors surround the specific sample area - if you remove the upper and lower squares in the lefthand image, the effect is much dimished (view at site) Just goes to show how we can't trust our eyes. If you've never made an object disappear in your eye's blind spot, I highly recommend trying it out!