public void TestMultiplyAlpha ()
{
var color = new Color (1, 1, 1, 1);
color = color.MultiplyAlpha (0.25);
Assert.AreEqual (.25, color.A);
color = Color.Default;
Assert.Throws<InvalidOperationException>(()=>color = color.MultiplyAlpha (0.25));
color = Color.FromHsla (1, 1, 1, 1);
color = color.MultiplyAlpha (0.25);
Assert.AreEqual (.25, color.A);
}