UIColor 和 NSString 类型的转换

NSString 类型对象@"redColor" 转换为 UIColor 对象： 

       SEL backColorSel = NSSelectorFromString(@"redColor");
        UIColor* backColor= nil;
        if ([UIColor respondsToSelector: backColorSel])
            backColor  = [UIColor performSelector:backColorSel];