Generate a random UIColor

[UIColor colorWithHue:drand48() saturation:1.0 brightness:1.0 alpha:1.0];

or in Swift:

UIColor(hue: CGFloat(drand48()), saturation: 1, brightness: 1, alpha: 1)

Feel free to randomise or adjust saturation and brightness to your liking.

Here is a swift version, made into a UIColor extension:

extension UIColor {
    class func randomColor(randomAlpha: Bool = false) -> UIColor {
        let redValue = CGFloat(arc4random_uniform(255)) / 255.0;
        let greenValue = CGFloat(arc4random_uniform(255)) / 255.0;
        let blueValue = CGFloat(arc4random_uniform(255)) / 255.0;
        let alphaValue = randomAlpha ? CGFloat(arc4random_uniform(255)) / 255.0 : 1;

        return UIColor(red: redValue, green: greenValue, blue: blueValue, alpha: alphaValue)
    }
}

Because you have assigned the colour values to int variables. Use float (or CGFloat) instead. Also (as @stackunderflow's said), the remainder must be taken modulo 256 in order to cover the whole range 0.0 ... 1.0:

CGFloat red = arc4random() % 256 / 255.0;
// Or (recommended):
CGFloat red = arc4random_uniform(256) / 255.0;