Returning and Formatting Exceptions

Question

I am trying to return exceptions and also formatting them, but I cannot seem to figure it out. What I want is when there is an error (Exception) to return it so I can display the error message. But I want different formats for an error and a success on form submit. As a simple test I am trying the following, but the

return $e->getMessage();

does not work. When I use

echo $e->getMessage();

it does work, but I want my error messages to be displayed in red, and when there are no errors, I want a "success" message in green, to keep it simple. But I do not want to format any HTML or CSS in my PHP class, obviously. I've checked google and searched on stackoverflow loads, but I cannot seem to figure it out, and is must be so simple.

Index.php

<?php
require 'myClass.php';

$myTest = new myClass();

    if (isset($_POST["submit"]))
    {
        $myTest->myCheck();
    }
?>

myClass.php:

    public function myCheck()
    {
        try
        {
            if (empty($this->myField)) {
                throw new Exception("Oops! Something went wrong. One or more of the fields were left empty");
            }

        return true;

        }

        catch (Exception $e)
        {
            return $e->getMessage();
        }
    }
}
?>