Fixes #65
Swift or Obj-C applications extending UIColor or NSColor like:

extension UIColor {
    func toHexString() -> String {
        return "#000000"
    }
}

would override the internal toHexString() which excludes the # and would cause a corrupt URL.
This method gets overridden because the class inherits from NSObject and therefore makes use of dynamic dispatching.

Note that Swift 4.0 in unaffected by this bug/feature.

@1ec5 👀