unsigned int count = 0;
        Ivar *ivars = class_copyIvarList([UIAlertAction class], &count);
        for (int i = 0; i<count; i++) {
            // 取出成员变量
            //        Ivar ivar = *(ivars + i);
            Ivar ivar = ivars[i];
            // 打印成员变量名字
            NSLog(@"%s------%s", ivar_getName(ivar),ivar_getTypeEncoding(ivar));
        }

获取了成员变量的名字之后，再去设置颜色
[alertAction setValue:titleColor forKey:@"titleTextColor"];