Background color of the background view

Just a wondering, why not replace the `backgroundStyle` and `backgroundOpacity` with one property `backgroundColor` ? 

Because an instance of `UIColor` has an alpha parameter and will be transparent if we use `[UIColor clearColor]`.

I just want to use another color as the background, and so it could be useful to simply the API here, but maybe you've already been through this idea, let me know.

Cheers