The thing is that when it comes to values, numbers and colors are interchangeable. Colors are made by values or numbers, if you want a 0 value somewhere, you can use the color black in its place, because the value for black is 0. And if you want a 1 value somewhere, you can use the color white and it will accept it since white is 1, 1, 1. So if you have Fresnel plugged in, it will go from white to black or you can also see it a going from 1 to 0 and there you have your values imputed for you.
