And it is because they contain.. oh bugger, I've already forgotten it. Something about fluorescent stuff that reflects back as many protons as it absorbs, and you would need a scanner with a black light source to read them, but then it would only read black and white as it couldn't reflect back any colour.
I had to highlite something just for the sensation of seeing the protons do their thing. But now I feel like they are cheating my eyes, and I don't understand why.
Have a sketch. I know were I am with a sketch.