This was kind of an interesting little article… mostly because I didn’t know we had some ladies with four types of cones on their retna than three. I feel seriously slighted by evolution now. 
http://www.cnn.com/2010/HEALTH/06/24/color.vision.evolution/
Anyway, color is my most often used example for illustrating the difference between “That which is apparent” and “That which really is.”
Black and White, for example. We all know from gradeschool that Black means all color is being absorbed and white means all color is being reflected.
But when you see black, or white, are you really seeing what you think you’re seeing? :ponder
If something is black, is it absorbing all colors? Or is it just absorbing those handful in our limited range of vision? We see a very narrow spectrum of light. What is black to us might be a bit more colorful to someone who can see a broader range of light.
The naked eye can’t tell the difference, and for most intents and purposes, it doesn’t matter anyway.
Our sky, however, only appears blue to us. Flies, which can see further into the ultraviolet spectrum than we can, observe a hue in the sky that is a bit more violet. (Or at least, so we surmise… I for one have never looked through the eyes of a fly.)