Swizzles in a randomized color block in place of the cgColor getter on UIColor, randomizing every color throughout the app. This WILL get you rejected from the App Store.

UIColor+UnsafeSwizzlingRandomizer.swift

public extension UIColor {

    private struct StaticVars {
        // Names of classes to swizzle. Derived from dumped private headers.
        static let classesToSwizzle: [String] = [
            "UIColor",
            "UIDeviceRGBColor",
            "NSColor",
            "UIDisplayP3Color",
            "UIPlaceholderColor",
            "UICIColor",
            "UIDeviceWhiteColor",
            "UICGColor",
            "UICachedDeviceRGBColor",
            "UICachedDeviceWhiteColor",
            "UICachedDevicePatternColor",
        ]

        static let randomColorBlock: @convention(block) (AnyObject?) -> CGColor = { (_: AnyObject?) -> (CGColor) in
            return CGColor(colorSpace: CGColorSpaceCreateDeviceRGB(), components: [
                CGFloat(Float(arc4random()) / Float(UINT32_MAX)), // R
                CGFloat(Float(arc4random()) / Float(UINT32_MAX)), // G
                CGFloat(Float(arc4random()) / Float(UINT32_MAX)), // B
                1.0, // A
                ])!
        }
    }

    private static let rzl_swizzleImplementation: Void = {

        for className in StaticVars.classesToSwizzle {
            if let classFromString = NSClassFromString(className),
                let originalMethod = class_getInstanceMethod(classFromString.self, #selector(getter: cgColor)) {
                method_setImplementation(originalMethod, imp_implementationWithBlock(unsafeBitCast(StaticVars.randomColorBlock, to: AnyObject.self)))
            }
        }

    }()

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

}

I made a new version of this that does the same thing (perhaps even more invasively), and probably won't get you rejected: https://gist.github.com/colejd/e41fc68f8335670999a7859df0d6fa93