iOS7以后系统提供了显示html标签的方法

UIKIT_EXTERN NSString *const NSHTMLTextDocumentType NS_AVAILABLE_IOS(7_0);

直接上代码

NSString *str = @"<font color="#6c6c6c">满20减5 满40减15，还剩<font color="#ff9147">113天";
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(30, 50, 300, 50)];
NSAttributedString *attrStr = [[NSAttributedString alloc] initWithData:[str dataUsingEncoding:NSUnicodeStringEncoding] options:@{NSDocumentTypeDocumentAttribute:NSHTMLTextDocumentType} documentAttributes:nil error:nil];
label.attributedText = attrStr;
//如果想要改变文字的字体,请在设置attributedText之后设置
label.font = [UIFont systemFontOfSize:20];
[self.view addSubview:label];