Here at Art of Play, we love optical illusions. Especially the unsuspecting kind like this photo of strawberries here. Believe it or not, there are no red pixels in this photo. What you're seeing is a combination of green and gray hues. Yea, we scratched our heads over that one for a while. We're made to see red through the scientific principle of color constancy, which famously applies to the classic checker shadow illusion by Edward H. Adelson below:
The squares marked A and B are the same shade of gray.