function hex2string(hex) {
    var hexString = hex.toString(16);
    hexString = '000000'.substring(0, 6 - hexString.length) + hexString;
    return "#" + hexString;
}
Converts a hexadecimal color number to a string.
@example
PIXI.utils.hex2string(0xffffff); // returns "#ffffff"
@memberof PIXI.utils
@function hex2string
@param {number} hex - Number in hex (e.g., `0xffffff`)
@returns {string} The string color (e.g., `"#ffffff"`).