Swift 3: CSS color names and hex to UIColor. UIColor from hex 3, 4, 6, and 8 characters in length with or without # prefix. UIColor to hex. UIColor extension that creates immutable UIColor instances from hexadecimal and CSS color name strings (e.g. ff0, #f00, ff0000, ff0000ff, Pink, aZure, CLEAR, nil). Conversely, you can obtain a UIColor's hexa…

UIColor.swift

//
//  UIColor.swift
//  previously Color+HexAndCSSColorNames.swift
//
//  Created by Norman Basham on 12/8/15.
//  Copyright © 2017 Black Labs. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import UIKit

public extension UIColor {

    /**
     Creates an immuatble UIColor instance specified by a hex string, CSS color name, or nil.

     - parameter hexString: A case insensitive String? representing a hex or CSS value e.g.

     - **"abc"**
     - **"abc7"**
     - **"#abc7"**
     - **"00FFFF"**
     - **"#00FFFF"**
     - **"00FFFF77"**
     - **"Orange", "Azure", "Tomato"** Modern browsers support 140 color names (<http://www.w3schools.com/cssref/css_colornames.asp>)
     - **"Clear"** [UIColor clearColor]
     - **"Transparent"** [UIColor clearColor]
     - **nil** [UIColor clearColor]
     - **empty string** [UIColor clearColor]
     */
    public convenience init(hex: String?) {
        let normalizedHexString: String = UIColor.normalize(hex)
        var c: CUnsignedInt = 0
        Scanner(string: normalizedHexString).scanHexInt32(&c)
        self.init(red:UIColorMasks.redValue(c), green:UIColorMasks.greenValue(c), blue:UIColorMasks.blueValue(c), alpha:UIColorMasks.alphaValue(c))
    }

    /**
     Returns a hex equivalent of this UIColor.

     - Parameter includeAlpha:   Optional parameter to include the alpha hex.

     color.hexDescription() -> "ff0000"

     color.hexDescription(true) -> "ff0000aa"

     - Returns: A new string with `String` with the color's hexidecimal value.
     */
    public func hexDescription(_ includeAlpha: Bool = false) -> String {
        guard self.cgColor.numberOfComponents == 4 else {
            return "Color not RGB."
        }
        let a = self.cgColor.components!.map { Int($0 * CGFloat(255)) }
        let color = String.init(format: "%02x%02x%02x", a[0], a[1], a[2])
        if includeAlpha {
            let alpha = String.init(format: "%02x", a[3])
            return "\(color)\(alpha)"
        }
        return color
    }

    fileprivate enum UIColorMasks: CUnsignedInt {
        case redMask    = 0xff000000
        case greenMask  = 0x00ff0000
        case blueMask   = 0x0000ff00
        case alphaMask  = 0x000000ff

        static func redValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & redMask.rawValue) >> 24) / 255.0
        }

        static func greenValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & greenMask.rawValue) >> 16) / 255.0
        }

        static func blueValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat((value & blueMask.rawValue) >> 8) / 255.0
        }

        static func alphaValue(_ value: CUnsignedInt) -> CGFloat {
            return CGFloat(value & alphaMask.rawValue) / 255.0
        }
    }

    fileprivate static func normalize(_ hex: String?) -> String {
        guard var hexString = hex else {
            return "00000000"
        }
        if let cssColor = cssToHexDictionairy[hexString.uppercased()] {
            return cssColor.characters.count == 8 ? cssColor : cssColor + "ff"
        }
        if hexString.hasPrefix("#") {
            hexString = String(hexString.characters.dropFirst())
        }
        if hexString.characters.count == 3 || hexString.characters.count == 4 {
            hexString = hexString.characters.map { "\($0)\($0)" } .joined()
        }
        let hasAlpha = hexString.characters.count > 7
        if !hasAlpha {
            hexString += "ff"
        }
        return hexString
    }

    /**
     All modern browsers support the following 140 color names (see http://www.w3schools.com/cssref/css_colornames.asp)
     */
    fileprivate static func hexFromCssName(_ cssName: String) -> String {
        let key = cssName.uppercased()
        if let hex = cssToHexDictionairy[key] {
            return hex
        }
        return cssName
    }

    fileprivate static let cssToHexDictionairy: [String: String] = [
        "CLEAR": "00000000",
        "TRANSPARENT": "00000000",
        "": "00000000",
        "ALICEBLUE": "F0F8FF",
        "ANTIQUEWHITE": "FAEBD7",
        "AQUA": "00FFFF",
        "AQUAMARINE": "7FFFD4",
        "AZURE": "F0FFFF",
        "BEIGE": "F5F5DC",
        "BISQUE": "FFE4C4",
        "BLACK": "000000",
        "BLANCHEDALMOND": "FFEBCD",
        "BLUE": "0000FF",
        "BLUEVIOLET": "8A2BE2",
        "BROWN": "A52A2A",
        "BURLYWOOD": "DEB887",
        "CADETBLUE": "5F9EA0",
        "CHARTREUSE": "7FFF00",
        "CHOCOLATE": "D2691E",
        "CORAL": "FF7F50",
        "CORNFLOWERBLUE": "6495ED",
        "CORNSILK": "FFF8DC",
        "CRIMSON": "DC143C",
        "CYAN": "00FFFF",
        "DARKBLUE": "00008B",
        "DARKCYAN": "008B8B",
        "DARKGOLDENROD": "B8860B",
        "DARKGRAY": "A9A9A9",
        "DARKGREY": "A9A9A9",
        "DARKGREEN": "006400",
        "DARKKHAKI": "BDB76B",
        "DARKMAGENTA": "8B008B",
        "DARKOLIVEGREEN": "556B2F",
        "DARKORANGE": "FF8C00",
        "DARKORCHID": "9932CC",
        "DARKRED": "8B0000",
        "DARKSALMON": "E9967A",
        "DARKSEAGREEN": "8FBC8F",
        "DARKSLATEBLUE": "483D8B",
        "DARKSLATEGRAY": "2F4F4F",
        "DARKSLATEGREY": "2F4F4F",
        "DARKTURQUOISE": "00CED1",
        "DARKVIOLET": "9400D3",
        "DEEPPINK": "FF1493",
        "DEEPSKYBLUE": "00BFFF",
        "DIMGRAY": "696969",
        "DIMGREY": "696969",
        "DODGERBLUE": "1E90FF",
        "FIREBRICK": "B22222",
        "FLORALWHITE": "FFFAF0",
        "FORESTGREEN": "228B22",
        "FUCHSIA": "FF00FF",
        "GAINSBORO": "DCDCDC",
        "GHOSTWHITE": "F8F8FF",
        "GOLD": "FFD700",
        "GOLDENROD": "DAA520",
        "GRAY": "808080",
        "GREY": "808080",
        "GREEN": "008000",
        "GREENYELLOW": "ADFF2F",
        "HONEYDEW": "F0FFF0",
        "HOTPINK": "FF69B4",
        "INDIANRED": "CD5C5C",
        "INDIGO": "4B0082",
        "IVORY": "FFFFF0",
        "KHAKI": "F0E68C",
        "LAVENDER": "E6E6FA",
        "LAVENDERBLUSH": "FFF0F5",
        "LAWNGREEN": "7CFC00",
        "LEMONCHIFFON": "FFFACD",
        "LIGHTBLUE": "ADD8E6",
        "LIGHTCORAL": "F08080",
        "LIGHTCYAN": "E0FFFF",
        "LIGHTGOLDENRODYELLOW": "FAFAD2",
        "LIGHTGRAY": "D3D3D3",
        "LIGHTGREY": "D3D3D3",
        "LIGHTGREEN": "90EE90",
        "LIGHTPINK": "FFB6C1",
        "LIGHTSALMON": "FFA07A",
        "LIGHTSEAGREEN": "20B2AA",
        "LIGHTSKYBLUE": "87CEFA",
        "LIGHTSLATEGRAY": "778899",
        "LIGHTSLATEGREY": "778899",
        "LIGHTSTEELBLUE": "B0C4DE",
        "LIGHTYELLOW": "FFFFE0",
        "LIME": "00FF00",
        "LIMEGREEN": "32CD32",
        "LINEN": "FAF0E6",
        "MAGENTA": "FF00FF",
        "MAROON": "800000",
        "MEDIUMAQUAMARINE": "66CDAA",
        "MEDIUMBLUE": "0000CD",
        "MEDIUMORCHID": "BA55D3",
        "MEDIUMPURPLE": "9370DB",
        "MEDIUMSEAGREEN": "3CB371",
        "MEDIUMSLATEBLUE": "7B68EE",
        "MEDIUMSPRINGGREEN": "00FA9A",
        "MEDIUMTURQUOISE": "48D1CC",
        "MEDIUMVIOLETRED": "C71585",
        "MIDNIGHTBLUE": "191970",
        "MINTCREAM": "F5FFFA",
        "MISTYROSE": "FFE4E1",
        "MOCCASIN": "FFE4B5",
        "NAVAJOWHITE": "FFDEAD",
        "NAVY": "000080",
        "OLDLACE": "FDF5E6",
        "OLIVE": "808000",
        "OLIVEDRAB": "6B8E23",
        "ORANGE": "FFA500",
        "ORANGERED": "FF4500",
        "ORCHID": "DA70D6",
        "PALEGOLDENROD": "EEE8AA",
        "PALEGREEN": "98FB98",
        "PALETURQUOISE": "AFEEEE",
        "PALEVIOLETRED": "DB7093",
        "PAPAYAWHIP": "FFEFD5",
        "PEACHPUFF": "FFDAB9",
        "PERU": "CD853F",
        "PINK": "FFC0CB",
        "PLUM": "DDA0DD",
        "POWDERBLUE": "B0E0E6",
        "PURPLE": "800080",
        "RED": "FF0000",
        "ROSYBROWN": "BC8F8F",
        "ROYALBLUE": "4169E1",
        "SADDLEBROWN": "8B4513",
        "SALMON": "FA8072",
        "SANDYBROWN": "F4A460",
        "SEAGREEN": "2E8B57",
        "SEASHELL": "FFF5EE",
        "SIENNA": "A0522D",
        "SILVER": "C0C0C0",
        "SKYBLUE": "87CEEB",
        "SLATEBLUE": "6A5ACD",
        "SLATEGRAY": "708090",
        "SLATEGREY": "708090",
        "SNOW": "FFFAFA",
        "SPRINGGREEN": "00FF7F",
        "STEELBLUE": "4682B4",
        "TAN": "D2B48C",
        "TEAL": "008080",
        "THISTLE": "D8BFD8",
        "TOMATO": "FF6347",
        "TURQUOISE": "40E0D0",
        "VIOLET": "EE82EE",
        "WHEAT": "F5DEB3",
        "WHITE": "FFFFFF",
        "WHITESMOKE": "F5F5F5",
        "YELLOW": "FFFF00",
        "YELLOWGREEN": "9ACD32"
    ]
}

Thank you very much! I've added your changes.