I've made a change for beta 2 so that you don't have to explicitly specify the wrapped "wings" color. It will simply inherit the background color. However, this isn't exactly how the default ones all appear though it's close.
Just to paste an example here:
Code:
.userBanner.bannerGray { color: black; background-color: gray; border-color: #AAA; }
.userBanner.bannerGray.wrapped span { background-color: #AAA; }
Note that the background colors are different, so if you want exactly this behavior, you will need to specify both the banner and the wrapped span.
However, as of beta 2...
Rich (BB code):
.userBanner.bannerGreen { color: white; background-color: green; border-color: green; }
.userBanner.bannerGreen.wrapped span { background-color: green; }
The second line there is superfluous because the wings have the same background color as the banner itself.