You only get two properties: a Color property (which actually is a Color, not a Brush) that let’s you change the color of the shadow, and a CornerRadius property that you can use to round off the corners on the dropshadow.
The good news is that this thing has pretty good perf. It’s just a bunch of drawing commands and gradients and all of it gets rendered in code in the OnRender override of the control.
SystemDropShadowChrome is in the Microsoft.Windows.Themes namespace. We tucked a lot of little gems away in this namespace. Basically anything that we needed to pull off a visual effect in the system themes, but which didn’t make sense as a first-class element in the platform, got tucked away in there. Everything is available for your tinkering pleasure. You’ll have to import the namespace though (and add a reference to one of the theme assemblies).
If you want to experience SystemDropShadowChrome in person, you can download a project here.