In 3.0, the property is modulate
, which combines color and transparency.
To tween the property, since the value is a Color, you have to give two colors as an argument. So to just fade the sprite you'd do this:
$Tween.interpolate_property($AnimatedSprite, "modulate",
Color(1, 1, 1, 1), Color(1, 1, 1, 0), 2.0,
Tween.TRANS_LINEAR, Tween.EASE_IN)