iPhone UIView Animation Duration only works instantly

Question

This code is being executed in the touchesended method of a subclassed uiview, however it doesn't animate, it just instantly changes the background color. What is wrong?

    self.backgroundColor = [UIColor blackColor];
    [UIView beginAnimations:nil context:NULL];

    [UIView setAnimationDuration:20];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
    if (score < .40) {
        self.backgroundColor = [UIColor redColor];
    } else {
        self.backgroundColor = [UIColor greenColor];
    }
    [UIView commitAnimations];