string color="Red"
string s = " xmlns='http://schemas.microsoft.com/client/2007'";
s+=" xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'" ;
s+=" Color='"+color+"'/>";
SolidColorBrush brush =(SolidColorBrush) XamlReader.Load(s);
LayoutRoot.Background = brush;