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

UIColor+InvasiveSwizzlingRandomizer.swift

import Foundation

/*
 ██████╗  █████╗ ███╗   ██╗ ██████╗ ███████╗██████╗     ███████╗ ██████╗ ███╗   ██╗███████╗
 ██╔══██╗██╔══██╗████╗  ██║██╔════╝ ██╔════╝██╔══██╗    ╚══███╔╝██╔═══██╗████╗  ██║██╔════╝
 ██║  ██║███████║██╔██╗ ██║██║  ███╗█████╗  ██████╔╝      ███╔╝ ██║   ██║██╔██╗ ██║█████╗
 ██║  ██║██╔══██║██║╚██╗██║██║   ██║██╔══╝  ██╔══██╗     ███╔╝  ██║   ██║██║╚██╗██║██╔══╝
 ██████╔╝██║  ██║██║ ╚████║╚██████╔╝███████╗██║  ██║    ███████╗╚██████╔╝██║ ╚████║███████╗
 ╚═════╝ ╚═╝  ╚═╝╚═╝  ╚═══╝ ╚═════╝ ╚══════╝╚═╝  ╚═╝    ╚══════╝ ╚═════╝ ╚═╝  ╚═══╝╚══════╝
 */

public extension UIColor {

    private struct StaticVars {
        static let randomColorBlock: @convention(block) (AnyObject?) -> CGColor = { _ -> (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 = {

        func isClassSubclassOf(_ base: AnyClass?, superclass: AnyClass) -> Bool {
            var _class: AnyClass? = base
            while _class != nil && _class != superclass {
                _class = class_getSuperclass(_class)
            }
            return _class == superclass
        }

        var classCount = objc_getClassList(nil, 0)
        var allClasses = UnsafeMutablePointer<AnyClass?>.allocate(capacity: Int(classCount))
        var autoreleasingAllClasses = AutoreleasingUnsafeMutablePointer<AnyClass?>(allClasses)
        classCount = objc_getClassList(autoreleasingAllClasses, classCount)

        for i in 0 ..< classCount {
            if let currentClass: AnyClass = allClasses[Int(i)],
                isClassSubclassOf(currentClass, superclass: UIColor.self),
                let originalMethod = class_getInstanceMethod(currentClass.self, #selector(getter: cgColor)) {
                method_setImplementation(originalMethod, imp_implementationWithBlock(
                    unsafeBitCast(StaticVars.randomColorBlock, to: AnyObject.self)))
            }
        }

    }()

    /**
     Swaps all UIColor.cgColor getter calls for a function block that returns a random color. This has the
     effect of randomizing all UIColors every time their getter is called.
     */
    public static func rzl_swizzle() {
        _ = self.rzl_swizzleImplementation
    }

}

To use, just call UIColor.rzl_swizzle() somewhere (AppDelegate, for example). Once is enough.

This will probably not get you rejected from the app store, but it is in poor taste.