Okay, I've given this a go (using the latest source code, but version 0.5.2.0 should work the same way):
var sampleDoc = SvgDocument.Open(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, @"..\..\sample.svg"));
sampleDoc.GetElementById<SvgUse>("Commonwealth_Star").Fill = new SvgColourServer(Color.Black);
It's simply a case of getting the required element (SvgCircle, SvgPath, SvgPolygon etc) and setting he Fill property of the element and that calling Draw().
I've added this to the Samples folder in the
latest check-in under the RuntimeUpdates folder so you can download and run the code (note that it depends on VS 2010 but should be an easy conversion to VS 2008).
Let me know if this isn't suitable for you.