通过给UIColor或者String添加extension都可以实现，以下列出两种方法：

给String添加extension

extension String{
    /// 将十六进制颜色转伟UIColor
    /// - Returns: UIColor
    public func toUIColor() -> UIColor {
      //处理数值
       var cString = self.uppercased().trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
        
       let length = (cString as NSString).length
        //错误处理
        if (length < 6 || length > 7 || (!cString.hasPrefix("#") && length == 7)){
           return UIColor.white
        }

        if cString.hasPrefix("#"){
           cString = (cString as NSString).substring(from: 1)
        }
        
        //字符chuan截取
        var range = NSRange()
        range.location = 0
        range.length = 2
        
        let rString = (cString as NSString).substring(with: range)
        
        range.location = 2
        let gString = (cString as NSString).substring(with: range)
        
        range.location = 4
        let bString = (cString as NSString).substring(with: range)
        
        //存储转换后的数值
        var r:UInt32 = 0,g:UInt32 = 0,b:UInt32 = 0
        //进行转换
        Scanner(string: rString).scanHexInt32(&r)
        Scanner(string: gString).scanHexInt32(&g)
        Scanner(string: bString).scanHexInt32(&b)
        //根据颜色值创建UIColor
        return UIColor(red: CGFloat(r)/255.0, green: CGFloat(g)/255.0, blue: CGFloat(b)/255.0, alpha: 1.0)
    }
}

给UIColor添加extension

extension UIColor{
    convenience init(hexString:String){
        //处理数值
        var cString = hexString.uppercased().trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
        
        let length = (cString as NSString).length
        //错误处理
        if (length < 6 || length > 7 || (!cString.hasPrefix("#") && length == 7)){
            //返回whiteColor
            self.init(red: 0.0, green: 0.0, blue: 0.0, alpha: 1.0)
            return
        }
        
        if cString.hasPrefix("#"){
            cString = (cString as NSString).substring(from: 1)
        }
        
        //字符chuan截取
        var range = NSRange()
        range.location = 0
        range.length = 2
        
        let rString = (cString as NSString).substring(with: range)
        
        range.location = 2
        let gString = (cString as NSString).substring(with: range)
        
        range.location = 4
        let bString = (cString as NSString).substring(with: range)
        
        //存储转换后的数值
        var r:UInt32 = 0,g:UInt32 = 0,b:UInt32 = 0
        //进行转换
        Scanner(string: rString).scanHexInt32(&r)
        Scanner(string: gString).scanHexInt32(&g)
        Scanner(string: bString).scanHexInt32(&b)
        //根据颜色值创建UIColor
         self.init(red: CGFloat(r)/255.0, green: CGFloat(g)/255.0, blue: CGFloat(b)/255.0, alpha: 1.0)
    }
}