The opacity of the single color used as background, between 0 (fully transparent) and 1 (opaque). Only when type is SINGLE_COLOR. For now, a semi-transparent color will reveal what's behind the HTML canvas of the Game on the webpage which isn't very useful. In the future, if people can integrate their dbb game in their own webpage, transparent background might come in handy.
The single color to use as background. Only when type is SINGLE_COLOR.