/**
 改变UILabel部分字符颜色
 */

- (void)setContentLabelColor {
    NSString *content = @"2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客\n2018-08-27\n写博客";
    NSMutableArray *locationArr = [self calculateSubStringCount:content str:@"\n"];
    NSMutableAttributedString *attstr = [[NSMutableAttributedString alloc] initWithString:content];
    for (int i=0; i<locationArr.count; i++) {
        if (i%2==0) {
            NSNumber *location = locationArr[i];
            [attstr addAttribute:NSForegroundColorAttributeName value:[UIColor colorWithRed:255.0f/255.0f green:45.0f/255.0f blue:81.0f/255.0f alpha:1.0f] range:NSMakeRange(location.integerValue-10, 10)];//改变\n前边的10位字符颜色，
        }
    }
    self.contentLabel.attributedText = attstr;
}

/**
 查找子字符串在父字符串中的所有位置
 @param content 父字符串
 @param tab 子字符串
 @return 返回位置数组
 */

- (NSMutableArray*)calculateSubStringCount:(NSString *)content str:(NSString *)tab {
    int location = 0;
    NSMutableArray *locationArr = [NSMutableArray new];
    NSRange range = [content rangeOfString:tab];
    if (range.location == NSNotFound){
        return locationArr;
    }
    //声明一个临时字符串,记录截取之后的字符串
    NSString * subStr = content;
    while (range.location != NSNotFound) {
        if (location == 0) {
            location += range.location;
        } else {
            location += range.location + tab.length;
        }
        //记录位置
        NSNumber *number = [NSNumber numberWithUnsignedInteger:location];
        [locationArr addObject:number];
        //每次记录之后,把找到的字串截取掉
        subStr = [subStr substringFromIndex:range.location + range.length];
        NSLog(@"subStr %@",subStr);
        range = [subStr rangeOfString:tab];
        NSLog(@"rang %@",NSStringFromRange(range));
    }
    return locationArr;
}

摘自：https://blog.csdn.net/feiyue0823/article/details/82114430