我正在尝试给段落标题上色，但是效果不好。有人能指出为什么不能给我的部分上色吗？考虑下面的例子：

---
title: "number_sections"
output:
  pdf_document:
    number_sections: yes
    toc_depth: 4
    toc: true
  header-includes:
     -\usepackage{color}
     - \usepackage{sectsty}
     - \allsectionsfont{\color{red}}  
   
---

# Main Section

The above section and the ones below should be red

## 2nd Level

### 3rd Level

# Second Section

## another section

### yet another

#### and the last one please