Instagram animated background color with CAGradientLayer
###Basic
let gradientLocations = [0.0, 1.0]
let frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.width);
gradientLayer1.locations = gradientLocations
gradientLayer1.startPoint = CGPointMake(0.0, 0.0);
gradientLayer1.endPoint = CGPointMake(0.25 , 0.25);
gradientLayer1.frame = frame;
gradientLayer2.locations = gradientLocations
gradientLayer2.startPoint = CGPointMake(0.0, 1.0);
gradientLayer2.endPoint = CGPointMake(1.0, 0.0);
gradientLayer2.frame = frame;
gradientLayer3.locations = gradientLocations
gradientLayer3.startPoint = CGPointMake(0.0, 0.0);
gradientLayer3.endPoint = CGPointMake(1.0, 1.0);
gradientLayer3.frame = frame;
gradientLayer4.locations = gradientLocations
gradientLayer4.startPoint = CGPointMake(0.0, 1.0);
gradientLayer4.endPoint = CGPointMake(1.0, 0.0);
gradientLayer4.frame = frame;
self.view.layer.insertSublayer(gradientLayer1, atIndex: 0);
self.view.layer.insertSublayer(gradientLayer2, atIndex: 1);
self.view.layer.insertSublayer(gradientLayer3, atIndex: 2);
self.view.layer.insertSublayer(gradientLayer4, atIndex: 3);
add 4 gradientLayer to the 4 corners