Xna 4.0 uses premultiplied alpha so your code is not right.... you should multiply the color by the alpha... but i'd do something similar to this:
float fadeDuration = 1;
float fadeStart = 1.4f;
float timeElapsed = 0;
Color StartColor = Color.White;
Color EndColor = Color.Transparent;
void Update(GameTime time)
{
float secs = (float) time.ElapsedTime.TotalSeconds;
timeElapsed += secs;
if (timeElapsed>fadeStart)
{
// Value in 0..1 range
var alpha =(timeElapsed - fadeStart)/fadeDuration;
Draw.Blender = Color.White * (1 - alpha);
// or Draw.Blender = Color.Lerp(StartColor, EndColor, alpha);
if (timeElapsed>fadeDuration + fadeStart)
{
Draw.Blender = EndColor;
// Change state
}
}
}