Swizzles in a randomized color block in place of the cgColor getter on UIColor, randomizing most colors throughout the app.

UIColor+SafeishSwizzlingRandomizer.swift

public extension UIColor {

    private static let rzl_swizzleImplementation: Void = {

        let instance: UIColor = UIColor.red // This is a `UICachedDeviceRGBColor` instance. For some reason you have to use red.
        let _class: AnyClass! = object_getClass(instance)

        let originalMethod = class_getInstanceMethod(_class, #selector(getter: cgColor))
        let swizzledMethod = class_getInstanceMethod(_class, #selector(rzl_randomCGColor))

        if let originalMethod = originalMethod, let swizzledMethod = swizzledMethod {
            method_exchangeImplementations(originalMethod, swizzledMethod)
        }
    }()

    public static func rzl_swizzle() {
        _ = self.rzl_swizzleImplementation
    }

    dynamic func rzl_randomCGColor() -> CGColor {
        return CGColor(colorSpace: CGColorSpaceCreateDeviceRGB(), components: [
            CGFloat(Float(arc4random()) / Float(UINT32_MAX)),
            CGFloat(Float(arc4random()) / Float(UINT32_MAX)),
            CGFloat(Float(arc4random()) / Float(UINT32_MAX)),
            CGFloat(Float(arc4random()) / Float(UINT32_MAX)),
            ])!
    }

}

I made a version that will replicate the functionality of the better, App-Store-unsafe way in a way that will probably not get you rejected: https://gist.github.com/colejd/e41fc68f8335670999a7859df0d6fa93