Spent a few minutes looking up the answer to this one:
I have an RGB color in traditional HTML Hex notation, like #1d5d8f. How do I create a SolidColorBrush in this color?
I’m sure I must be missing something easier, but here’s the C# code to do it:
byte r = System.Convert.ToByte("1d", 16);
byte g = System.Convert.ToByte("5d", 16);
byte b = System.Convert.ToByte("8f", 16);
Color s = Color.FromRgb(r, g, b);
Brush b = new SolidColorBrush(s);
The Pursuit of a Life 
…and, in Silverlight 2.0 b2:
public Color getColorFromHexString(string s)
{
byte a = System.Convert.ToByte(s.Substring(0, 2), 16);
byte r = System.Convert.ToByte(s.Substring(2, 2), 16);
byte g = System.Convert.ToByte(s.Substring(4, 2), 16);
byte b = System.Convert.ToByte(s.Substring(6, 2), 16);
return Color.FromArgb(a, r, g, b);
}