Sometimes color can really surprise you... It wasn't until doing the color study of this brilliant alley in San Miguel de Allende, México that I realized this photograph had a rainbow palette. When looking at the photograph I see orange, yellow, blue, and a little grey in the concrete. But when you look for actual colors in the photograph you see that the door is actually a redish hue and the underside of the awning an apple green. Not only can shadow change color like this but the mere placement of colors beside each other shifts our perception. Though, logically, I know that the door is probably stained wood (you can see the grain if you look closely) it appears orange at first next to the orange door jamb and then secondly I find that one of the colors of the door in the photograph is actually a brick red. Josef Albers is the king of this concept and you can read more about it in the revised edition of his book Interaction of Color.
This color theory stuff is crazy!