var color = Xamarin.Forms.Color.Orange;
int red = (int) (color.R * 255);
int green = (int) (color.G * 255);
int blue = (int) (color.B * 255);
int alpha = (int)(color.A * 255);
string hex = String.Format("#{0:X2}{1:X2}{2:X2}{3:X2}", red, green, blue, alpha);