Allowing User Customization of the Visual Bell

I came across this thread in which custom bell sounds were added, and realized that it could also be useful to customize the visual bell as well. I think the most straightforward customizations would be:

1. Allow changing the color, intensity, and duration of the default behavior (for instance, a normally black terminal flashing red briefly instead of grey) and/or
2. Adding, or overriding any background image with one indicating failure (see below)