U disk / U disk that displayed storage

There's matal grease on each side of the U disk,so we can avoid inserting U disk wrong that can not read the data inside.
The U disk surface's color will changing as the starage volume increased or decreased. When storage volume left less than one third, the surface color is a green smiling face; between one third and two thirds, it will be a orange normal face;while the storage volume left more than two thirds , the surface color is red, and the expression was a painfull face.