UIColor_Hex.swift

import UIKit

extension UIColor {

    convenience init?(hexRed red: Int, green: Int, blue: Int, alpha: Int = 255) {
        guard red >= 0 && red <= 255 else { return nil }
        guard green >= 0 && green <= 255 else { return nil }
        guard blue >= 0 && blue <= 255 else { return nil }

        self.init(red: CGFloat(red) / 255.0,
                  green: CGFloat(green) / 255.0,
                  blue: CGFloat(blue) / 255.0,
                  alpha: CGFloat(alpha) / 255.0)
    }

    convenience init?(hexString: String) {
        let hex = hexString.trimmingCharacters(in: CharacterSet.alphanumerics.inverted)
        var int = UInt32()
        Scanner(string: hex).scanHexInt32(&int)
        let red, green, blue, alpha: UInt32
        switch hex.characters.count {
        case 3: // RGB (12-bit)
            (alpha, red, green, blue) = (255, (int >> 8) * 17, (int >> 4 & 0xF) * 17, (int & 0xF) * 17)
        case 6: // RRGGBB (24-bit)
            (alpha, red, green, blue) = (255, int >> 16, int >> 8 & 0xFF, int & 0xFF)
        case 8: // AARRGGBB (32-bit)
            (alpha, red, green, blue) = (int >> 24, int >> 16 & 0xFF, int >> 8 & 0xFF, int & 0xFF)
        default:
            return nil
        }
        self.init(hexRed: Int(red), green: Int(green), blue: Int(blue), alpha: Int(alpha))
    }

}