Swift 16 进制颜色字符串转 UIColor

import Foundation
import UIKit

extension UIColor {
    
    public convenience init?(hexString: String) {
        self.init(hexString: hexString, alpha: 1.0)
    }
    
    /**
     Create non-autoreleased color with in the given hex string and alpha.
     - parameter hexString: The hex string, with or without the hash character.
     - parameter alpha: The alpha value, a floating value between 0 and 1.
     - returns: A color with the given hex string and alpha.
     */
    public convenience init?(hexString: String, alpha: Float) {
        var hex = hexString
        
        // Check for hash and remove the hash
        if hex.hasPrefix("#") {
            hex = hex.substringFromIndex(hex.startIndex.advancedBy(1))
        }
        
        if (hex.rangeOfString("(^[0-9A-Fa-f]{6}$)|(^[0-9A-Fa-f]{3}$)", options: .RegularExpressionSearch) != nil) {
            
            // Deal with 3 character Hex strings
            if hex.characters.count == 3 {
                let redHex   = hex.substringToIndex(hex.startIndex.advancedBy(1))
                let greenHex = hex.substringWithRange(Range<String.Index>(start: hex.startIndex.advancedBy(1), end: hex.startIndex.advancedBy(2)))
                let blueHex  = hex.substringFromIndex(hex.startIndex.advancedBy(2))
                
                hex = redHex + redHex + greenHex + greenHex + blueHex + blueHex
            }
            
            let redHex = hex.substringToIndex(hex.startIndex.advancedBy(2))
            let greenHex = hex.substringWithRange(Range<String.Index>(start: hex.startIndex.advancedBy(2), end: hex.startIndex.advancedBy(4)))
            let blueHex = hex.substringWithRange(Range<String.Index>(start: hex.startIndex.advancedBy(4), end: hex.startIndex.advancedBy(6)))
            
            var redInt:   CUnsignedInt = 0
            var greenInt: CUnsignedInt = 0
            var blueInt:  CUnsignedInt = 0
            
            NSScanner(string: redHex).scanHexInt(&redInt)
            NSScanner(string: greenHex).scanHexInt(&greenInt)
            NSScanner(string: blueHex).scanHexInt(&blueInt)
            
            self.init(red: CGFloat(redInt) / 255.0, green: CGFloat(greenInt) / 255.0, blue: CGFloat(blueInt) / 255.0, alpha: CGFloat(alpha))
        }
        else {
            // Note:
            // The swift 1.1 compiler is currently unable to destroy partially initialized classes in all cases,
            // so it disallows formation of a situation where it would have to.  We consider this a bug to be fixed
            // in future releases, not a feature. -- Apple Forum
            self.init()
            return nil
        }
    }
}

https://github.com/thii/SwiftHEXColors/blob/master/Sources/SwiftHEXColors.swift