ColorRect only displays one color so you'll have to use a shader for this. You will have one input: the amount you want to wipe (between 0 and 1). This should work:
shader_type canvas_item;
uniform float amount : hint_range(0, 1) = 0.0;
void fragment() {
COLOR.a = max(0.0, min(1.0, 1.0 - amount + UV.x - mix(0.0, 1.0, amount)));
}
You can test it by moving the amount
slider in the Inspector. Then you can animate that property using AnimationPlayer.
You can obviously get a lot fancier with, but this is a plain linear wipe effect.