I see that the email clause generates the following html (note the class):
<a href="mailto:dummy@gmail.com" class="email">dummy@gmail.com</a>
Therefore you can change the color for (all parts of the document with) this class with (note the style section):
---
title: "my title"
author:
- name : "Mohamed_Fergany"
email: dummy@gmail.com
date: "28 Feb 2022"
output: html_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
<style>
.email {
color: red;
}
</style>
start of the actual document