7 year old, 5 year old, and I were eating lunch together and the 7 year old asked me "Mommy what is the darkest color?" Me:"I think it is black" Him:"But what shade of black?" Me:"Does black have multiple shades?" Him:"Well, when I color with a black crayon, I can keep coloring over something I have completely colored and it still seems to get darker" Me:"Ah, yes crayons do not cover completely in a single layer, there are spots of color and spots of blank in each layer, so as you color more layers on tops, each one will cover more of the original blank spots to get darker and darker. Now if you colored with a black marker, you would cover it up in a single layer at once" Him:"So mom even when you color layer after layer with a black crayon you will never cover up all the blank spots completely, well you might cover to the point the human eye sees it as covered, but if you looked under a microscope you would see there are still spots blank all the way down to the paper, right mom?" Me:"Yes, that is correct, great thinking about the layers of spot coverage, now please finish your taco".