Is my Blue your Blue?

I remember I was in pre-school when I learned what red was. My teacher held up an apple and very deliberately said, "this is an apple and it is red". I was enlightened. Red is the color of apples. It wasn't until a little while later my world came crashing down on me. Granny Smiths are apples but they aren't red. Anyhow, for argument sake, lets consider the apple to be red. I took my teacher's word as gospel fact and I learned a valuable lesson. I now knew what red was because of the association with the apple.

Now let's consider for a moment, my classmates. They were at the same time being told what the color red was and how to identify it. My question now, after 25 years, is what if they didn't see the same red that I was seeing? I'm not talking about different shades but different colors altogether. What if little Johnny was actually seeing blue? He has been told that the name for what he is seeing is red. So, he calls it red. He sees, what I would say is, a blue apple, but he doesn't know it's not the same color as I'm seeing because he was taught that it is red. So the question would be, who can prove that we all see colors the same? The stop light is red and we go on green. What is green? Would you be shocked at what you were seeing if you were in my head looking out through my eyes. Ok, it can be measured to a certain degree because of what we know about the frequency of light and color and how our eyes detect them. But ponder for a moment what I've said. Take this same idea and apply it to other things. Smell? Sound? Dreams? Birth defects? Please don't blame me if you can't sleep at nights.