Q: How to check color font in php for checking data form

This is what I did in my php but the color is in black

Code:
if(isset($_POST['email']))
{
 $email=$_POST['email'];

 $checkdata=" SELECT email FROM registration WHERE email='$email' ";

 $query=mysqli_query($db,$checkdata);
 if(mysqli_num_rows($query)>0){

  echo "Email Already registered";
...