Indeed the background property does not render the selected color. Nor do the other style properties. We will implement these properties in one of our next releases. Sorry for the inconvenience caused.
Of course, you can style your poll without these properties. All you need to do is set CssClass for the PollBox and do the styling through CSS. Thus you can also remove the numbers from the answers. By setting
for the list html element.
Hope this will help.