What color is white?
I'm going back the very beginning with this one. I just had my painter's birthday. Four years ago, I picked up a paintbrush, dipped it in some paint, and smeared it onto a canvas. I painted a tree that night. My homework after that class was to paint another tree. The next week, the art lesson was to paint something black and white. I did a cup... but it was awful, truly awful! I don't believe I have the courage to post a picture of it. The third week, we had to paint something white, and the lesson was to see that white wasn't white at all - but filled with colors.
This is a concept that still amazes me.