Custom field on home.php

Hello,

I’m using a custom field to change the colour of the header on all pages. Problem is, the home.php doesn’t qualify as a Page.

Even if I change

<?php
/**
 * The Template for displaying all single posts.
 *
 */
?>

To

<?php
/**
 * Template Name: Groups
 */
?>

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If I choose this template in the admin, with the Groups page, and fill in the custom field it appears to just use the index.php, which I don’t want.

At the moment it seems nigh impossible to achieve this? any thoughts?